Calls and Lines Connectivity

SIP2SIM Mobile extensions

The SIP2SIM service is a very simple concept which provides you with control of your mobile communications. It is ideal for an office of any size and even for more technical home users.

The service consists of a SIM card, which you put in a 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.


Not a SIP application

It is important to realise that we are not talking about a SIP application on a smart phone which then uses mobile data or WiFi. With this service your mobile phone is working as a mobile phone on the GSM mobile network making and receiving proper mobile voice calls. The SIP part is what we do in the back end to pass the calls to and from your SIP server.

An extension on your office phone system

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

This means your phone can simply be 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.
  • 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.

Manage costs

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.

  • £5+VAT to purchase the SIM card.
  • £2+VAT pcm once activated (activates on first use).
  • 2p+VAT per minute for calls either way.
  • 2p+VAT per text either way.
  • 2p+VAT per MB for data usage either way.
  • 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 some cases a SIM will be set up with a free trial which allows some usage without assigning to an account or setting up an account. For these trial SIMs, once assigned to an account an activation fee of 1p+VAT is charged and usage charges commence as normal.

OFCOM call charges

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.

Telephone numbers

Just like a SIP handset, the service does not come with any sort of telephone number.

You can, if you wish, have the phone register on a VoIP provider’s service. This would mean you get calls to a number operated by the VoIP provider, and can make calls from that number, just like any other SIP phone. If registered with your own telephone system, it would have internal extension numbering, and even direct dial in numbering as you have chosen to configure on your phone system.

There is no question of porting numbers to or from the service, it has no numbers.

We can, of course, provide telephone numbers as part of our VoIP service if you wish, and we can even pre-configure these to connect with your SIM as part of the order process.

International roaming

The SIMs are available with world wide roaming. Costs are higher when roaming, obviously. The following are charges for use within EU. See full roaming price list for more details.

  • £5+VAT to purchase the SIM card.
  • £2+VAT pcm once activated (activates on first use).
  • 10p+VAT per minute for calls either way.
  • 5p+VAT per text either way.
  • 10p+VAT per MB for data usage either way.
  • No minimum term – just monthly rolling contract.

In the UK and rest of EU, 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.

UK roaming for the best coverage of the UK

The SIMs can even roam in the UK. This means the SIM can change its identity automatically – being an O2 SIM when O2 is available (at the lowest costs), but switching to a foreign identity (Dutch Vodafone) to roam on to other UK networks. Whist costs are then higher this means you stay in touch even when there is no O2 signal.

When the SIM is using the O2 profile and on O2 in the UK, the UK prices apply. When using the EU profile on any UK network (including O2) or elsewhere in the EU, the EU roaming prices (as above) apply. If on EU profile on O2, it will normally switch back to O2 profile automatically within a few minutes. Currently the SIM will not roam to Three in the UK.


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).

Mobile Data

Data currently allows simple NAT, unfiltered, Internet access. We hope to offer data via A&A in the future.

Third Party SIP services

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.

The Sip2Sim service is provided by Andrews and Arnold Ltd  and can be purchased direct from them or via ourselves where we will assist with setting up the service for you.