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Switching to a cloud phone system: keeping your number, 999 and staying online

Moving to a cloud phone system is mostly paperwork and timing. The parts that catch small businesses out are moving the number customers already know, making sure 999 still works and knows where you are, and deciding what happens when the broadband drops. This guide covers each, with the rules Ofcom sets and what providers say on their own pages.

Facts checkedSources: Ofcom, GOV.UK, providers' own pages

Keeping your number

Number porting moves an existing number from your current provider to the new one. The number stays the same, so nothing needs reprinting and callers notice nothing. You ask the new provider (the "gaining" provider) and it deals with the old one. Ofcom's switching rules require that for business customers too, though the One Touch Switch system that home customers use is only compulsory for residential switches (Ofcom switching statement).

What Ofcom guarantees

Ofcom's General Condition C7 gives business customers these protections (Ofcom, General Conditions that protect business customers):

  • Porting must be offered on reasonable terms, and you can't be charged directly for porting your number.
  • You can still port a number for at least one month after you've switched away from the old service.
  • If a port fails, the number and its services have to be switched back on until the port succeeds.
  • The switch happens on the date you ask for where that's technically possible, and otherwise no later than one working day after the checks and activation are done. Any loss of service during the switch must not last more than one working day.

How long it takes

Ofcom's one working day starts after the checks, so it isn't the whole wait. The checks are where the time goes, and providers say so plainly. CircleLoop says a landline number can take "anything from a week to a month" to port (CircleLoop). Vonage says its process takes "a minimum of 20 business days and can be significantly longer" (Vonage). Mobile numbers are quicker: you get a PAC from your mobile network and CircleLoop puts the move at 1 to 2 business days. If the number matters to your business, allow a month and don't fix a go-live date until the new provider confirms the port date in writing.

The letter of authority

For a landline or VoIP number there's no PAC. Instead the new provider sends a letter of authority (LOA), a form that lets it ask your current provider to release the number. It has to be signed by the person who holds the account: Vonage asks for it on company headed paper, signed by the current account holder (Vonage), and RingCentral asks for the signed form with a copy of your latest bill (RingCentral). The name, address and numbers on it must match what your current provider holds. RingCentral warns that any mismatch delays the transfer, so copy the details from a recent bill rather than typing them from memory.

What can go wrong

  • Details that don't match. A different spelling of the business name, an old address or a missing number is the usual reason a port is rejected. A rejected request has to be corrected and sent again, which adds days.
  • Cancelling too early. CircleLoop and Vonage both say not to cancel your current service before the number has moved, because you can lose the number (CircleLoop, Vonage). Let the port end the old service, then cancel anything left over.
  • Losing your broadband. Porting the main number on a copper line usually closes that line. Vonage says that if your broadband is ADSL or FTTC on the same line, you will lose it when the number transfers; cable, full fibre (FTTP) and wireless connections aren't affected. CircleLoop gives the same warning about the main billing number. If your broadband runs over the phone line you're porting, get new broadband in first.
  • Numbers that can't move. CircleLoop says most geographic numbers can be ported, some non-geographic and freephone numbers only from certain providers, and premium rate numbers not at all (CircleLoop). Ask the new provider to check every number before you sign.
  • Exit fees. Porting doesn't cancel your old contract terms. Check the end date and any early termination charge before you set a date.

999 and 112 on a cloud phone system

Every provider of phone services has to let all users call 999 and 112 free of charge (General Condition A3.4, Ofcom General Conditions). What changes with an internet phone is how the emergency services find you.

Register the right address

A copper line was tied to one building. A cloud phone can be used anywhere, so the provider relies on the address you give it. Under General Condition A3.6, a provider of internet calls used mainly at one place must recommend that you register that address before the service starts and update it if it changes. Where the service is used from more than one place, it must recommend you update the location each time you use it somewhere new (Ofcom General Conditions). In practice that means registering each office's full address for its desk phones, and checking with the provider how location works for staff calling from the app at home or on the road. Providers also have to tell you about any limits on emergency calls when you buy, in their terms and in any user guide.

Power cuts and battery backup

Digital landlines need mains power and won't work in a power cut unless there's a battery backup (Ofcom). Ofcom's guidance says each provider should have at least one solution, such as a battery backup unit, that gives at least one hour of access to the emergency services in a power cut, and offer it free to customers who depend on their landline, for example because they have no mobile or no reliable mobile signal (Ofcom power cut guidance). In a 2024 letter to business providers, Ofcom said few business customers rely on a business line alone to call 999, but gave a sole trader working from home and a small office with no mobile signal as cases where that protection is likely to be needed (Ofcom letter). If that's you, tell the provider before you switch.

GOV.UK says a battery backup unit typically keeps a broadband router running for 4 to 7 hours, and that a 999 call from a mobile automatically uses another network if your own isn't available. If 999 won't connect from a mobile, try 112 (GOV.UK). For most small offices, a charged mobile is the practical fallback.

The switch-off deadline

Openreach closes the old analogue network on 31 January 2027, so anything still on a copper line, such as alarms, lift phones, door entry and older card terminals, needs checking whether or not you move your phones. Our PSTN switch-off guide covers what to check and the charges for leaving it late.

When the internet goes down

A cloud phone system is only as reliable as the connection under it. If the office broadband fails, desk phones go quiet, but calls don't have to be lost. These are the usual ways to keep answering:

  • Mobile apps. Staff can answer the business number on their own phones over mobile data. Of the 13 UK providers we list, the pricing pages of Aircall, bOnline and RingCentral RingEX mention a mobile app (as read on 3 November 2026); the others may have one too, so ask.
  • Call forwarding and failover rules. Ask the provider whether you can set where calls go when a phone or the whole office can't be reached, such as to a mobile, another site or voicemail, and what triggers it. Set it up on day one rather than during an outage.
  • A 4G or 5G backup connection. A router with a mobile data SIM can take over when the fixed line drops. Check it carries voice calls cleanly and that your phones and router switch to it on their own.
  • Power for the network kit. A small uninterruptible power supply on the router, the network switch and any phones powered over the network cable keeps calls going through short power cuts. It doesn't replace the emergency backup above.

A migration plan for a small business

Start with what you have

Get your latest phone bill and list every number on it, including any you've forgotten you pay for. Note who the account holder is, the contract end date and any exit charge. Walk round the building and note anything plugged into a phone socket: alarms, card machines, lift phones, a fax. Those need their own answer before the switch-off.

Check the broadband

Work out whether your broadband runs over the line you're porting. If it does, order replacement broadband first and move to it before the port. Make sure the connection has room for calls at your busiest time.

Choose the provider and plan

Compare the providers on published prices in the comparison table and work out a monthly figure for your own users, numbers and minutes in the cost calculator. Before you sign, ask the provider to confirm every number can be ported, how long it expects the port to take, and what emergency call and battery backup arrangements it offers.

Set up before you move the number

Get the new system working on a temporary number first. Vonage won't accept a port request until your phones have made and received a call (Vonage), and it's a sensible test with any provider. Register each site's address for emergency calls, install the app for anyone who works away from the desk, and set up your menus, voicemail and forwarding rules.

Request the port

Fill in the letter of authority with the details exactly as they appear on your bill, have the account holder sign it, and send it with a copy of the bill if the provider asks. Keep the old service running. When the provider gives you a port date, pick a quiet day if you can and tell staff what will happen.

On the day

Once the provider confirms the number has moved, call it from a mobile, check it rings where it should, make an outbound call and check the number the other person sees. Try the menu and leave a voicemail. Don't make a test call to 999.

Afterwards

Check the old provider stops billing for the ported number and cancel anything you no longer need; CircleLoop points out that this is your job, not the new provider's (CircleLoop). Write down what to do if the internet fails, keep emergency addresses up to date when people move office or start working from home, and look again at your alarms and card machines before 31 January 2027.

This guide reports what Ofcom, GOV.UK and the providers named publish. It isn't advice about your own setup. Check the details with your provider before you switch.