SIP2SIM®: Putting you in control of your office mobile

Mobile Voice (SIP2SIM®)

The SIP2SIM service is due to close at the end of April. Find out more.

Our SIP2SIM® service consists of a SIM card, which you put in an ordinary dumb mobile phone and it makes that phone appear as if it is a SIP extension (e.g. SIP phone) on a phone system of your choice.

Technical Information

An overview of SIP2SIM®

Not a mobile app!

SIP2SIM® is not a SIP app running on a smart phone over mobile data or WiFi! Having tried to make this work reliably, this was determined to be unpredictable at best, and completely useless at worst.

With this service your mobile phone is working as a mobile phone on the GSM mobile network; making and receiving proper mobile voice calls. GSM is a very mature technology, adept at handling changeovers between masts and packet loss, without breaking up.

Old and New

In SIP2SIM® we fuse the best of the old (GSM; reliable, stable) with the best of the new (SIP; flexible) in the network, and offer that to you as a service that you can build into your own PBX or value-added service.

Simple SIP2SIM iagram

It's just a (mobile) SIP device

The SIP2SIM® service makes your mobile work like a SIP device connected to a SIP phone system or VoIP provider of your choice. It can also be supplied pre-configured to an A&A VoIP number making your mobile work like a normal mobile phone but with a landline-style number.

Pricing Overview (non roaming)

SIM Card £5.00 +VAT Learn more

To purchase the SIM card (+Postage)

£5.00 +VAT per SIM
Monthly £2.00 +VAT Learn more

Once activated (activates on first use)

£2.00 +VAT per month
Airtime 2p +VAT Learn more

For calls either way between the SIM and the SIP endpoint. Further call charges may be imposed by the VoIP provider for outbound calls.

2p +VAT per minute
SMS 2p +VAT Learn more

Per text either way

2p +VAT per SMS
Data 2p +VAT Learn more

Data usage either way

2p +VAT per MB
  • Charges apply to the SIP2SIM service separately from any charges you may have for text or voice calls using your VoIP/SMS provider.
  • Calls are charged per second, and data per kilobyte (min 6kB per data session).
  • No minimum term - just monthly rolling contract.

An extension on your office phone system

The basic service allows you to specify, via our control pages, the server name, login and password for a SIP server. This could be your office phone system; an asterisk box, 3CX, FireBrick or similar.. As long as it handles normal UDP SIP with G.711 A-law audio then the service will register to it as a phone and allow calls both ways.

This means your mobile handset becomes an office extension, like any other.

  • Call office extensions using short extension numbers from your mobile phone.
  • Office policies on callable numbers, such as premium rate, enforced like any other extension.
  • Office voicemail system working, just like any other extension.

(Note, CLI shown on mobiles may be limited due to recent OFCOM rules)

  • Office call logging, just like any other extension.
  • Office call recording, just like any other extension.
  • Use in hunt groups, just like any other extension.
  • Even use features like call steal to transfer calls if you want, or in-band DTMF to control call transfer and related features.

Example Uses

Here is where you may find a use for SIP2SIM®

Man with a Phone

Employees have the same extension at desk and when mobile

Some people spend as much time out on the road as in the office. By using a SIP2SIM®, your extension number can be set to ring both your desk phone and the mobile, making it easy for customers and colleagues to contact you.


Ensure Mobile calls are recorded

As the SIM has the same feature set as any other SIP phone connected to the PBX, then features such as call recordings are also possible. Ideal for solicitors, those in the finance industry and others, whose regulatory requirements ensure they have a copy of their phone calls.

Three types are available:

UK-only O2 SIM

This SIM is single profile and works on O2 in the UK only.

  • Buy SIM £5.00 +VAT
  • Monthly SIM rental: £2.00 +VAT
  • Calls 2p +VATmin (Mobile leg)
  • Texts 2p +VAT
  • Data 2p +VAT/MB

Roaming O2/EU SIM

This SIM is dual profile allowing UK use at the 'O2 only' SIM pricing, and roaming abroad at the 'EU' SIM pricing.

  • Buy SIM £5.00 +VAT
  • Ongoing charges £2.00 +VAT pcm
  • Calls (O2) 2p +VAT/min (EU) 10p +VAT/min (Mobile leg)
  • Texts (O2) 2p +VAT (EU) 5p +VAT
  • Data (O2) 2p +VAT/MB (EU) 10p +VAT/MB

See roaming prices.

Roaming EU-only SIM

This SIM is fixed on the EU roaming profile, so does not use the lower O2 pricing even when using the O2 network. It will, however, roam onto multiple UK mobile networks, giving potentially greater coverage.

  • Buy SIM £5.00 +VAT
  • Ongoing charges £2.00 +VAT pcm
  • Calls 10p +VAT/min (Mobile leg)
  • Texts 5p +VAT
  • Data 10p +VAT/MB

See roaming prices.

Further Information

Below is further information about the service:

The costs are very simple for using the SIM in the UK on O2. Higher costs apply for roaming SIMs, even roaming to other UK networks.

  • No minimum term - just monthly rolling contract.
  • Calls are charged per second, and data per kilobyte.
  • Charges apply to the SIP2SIM® service separately from any charges you may have for text or voice calls using your VoIP/SMS provider.

In other words, there are two costs involved:

  1. The mobile leg (ie from the SIM to us, we then register to your VoIP provider, that may be our VoIP service or a third party).
  2. The cost that your VoIP provider charges to make calls.

The SIP2SIM® service is not a service that allows calls to telephone numbers in the national dialling plan. It allows calls to be passed to a VoIP/SIP gateway of your choice. Any ability to make calls to normal telephone numbers is provided by that VoIP provider (which may be our VoIP service). As such, special rules on costs of 01, 02, 03 numbers, rules on 0800 numbers being free, and rules on charges for other special and premium rate numbers do not apply to the SIP2SIM part of the service. The cost or the SIP2SIM® service applies regardless of the number you dial.

Texts are operated separately. Our text interface using HTTP can send texts to the phone, and texts from the phone can be posted to an HTTP gateway of your choice. If you have an A&A VoIP telephone number then texts can be associated with that number directly (not all of our numbers ranges can handle inbound texts).

Calling 999 and 112 is possible.

Learn More

The 3G data service provides simple NAT, unfiltered, Internet access. The voice part of the service doesn't use data but uses the normal mobile voice network. Data is provided over 3G. There are plans in the carrier to introduce 4G Voice (VoLTE) however this won't be available until at least 2023.

The service involves entering SIP registration details in to our control pages. Where these are the details of your own SIP server such as an office phone system, you can make the decision as to whether or not you trust us with those SIP details in order to provide the SIP2SIM® service. We will, of course, use all reasonable skill and care to ensure the details remain confidential and are not disclosed.

We have, however, designed the service so that it can work with a wide variety of third party SIP services, not just in the UK but in various countries. There are a lot of unusual systems out there and we continue to work to ensure that such services operate with SIP2SIM®. However, using third party SIP details may well be in breach of your terms with the third party SIP provider as it means giving us your SIP details. It is up to you to check the terms and we would not suggest anyone breaks a contract they have. You may find that the provider is happy to trust us, especially if they do any other work with us, so it is worth asking. We are also happy to discuss contracts with other providers for the SIP2SIM® service and we may be able to provide them with branded SIMs to sell to their customers.

Unfortunately we cannot guarantee that the service will always work with all other providers, and whilst we aim to resolve any technical issues (with reference to the standards), if a provider simply will not deal with our service and blocks us there is little we can do.

Branded SIM

Our voice and data SIM cards are ideal for a corporate network or for a wholesale customer to set up their own mobile service.

We can offer branding with professional quality SIM printing and pre-set settings.

Find our more

Technical details

We have a page with comprehensive list of technical details and restrictions and further articles in the knowledge base article which can be seen below.

Contact Sales

phone 03333 400222
(Mon-Fri 9am-5pm)
sms 01344 400222

Contact Support

phone 03333 400999
(Mon-Fri 8am-6pm,
Sat 10am-2pm)
sms 01344 400999