GSM mobile phone as a FreePBX extension – SIP2SIM

I’m testing an interesting product this week from a company called Andrews & Arnold. It’s a way of using a UK GSM mobile phone with FreePBX/Asterisk that I’ve not seen before.

The service is a PAYG “SIM only” mobile phone service. You get a SIM card to go in your existing mobile phone, which must be either unlocked or on the O2 network –


The difference with this SIM is that you don’t get a phone number attached to it, you get access to a SIP to GSM gateway. This means your mobile phone can be used the same as an other extension on FreePBX. You set up a SIP extension in FreePBX in the normal way, and then in the Andrews and Arnold (AA) portal you register the SIM as the extension –

AA SIP2SIM portal

FreePBX then passes calls to the AA SIP/GSM gateway and it talks to the SIM in the phone. This is different to running a SIP client on your mobile phone which uses 3G/4G/WiFi to make calls. Voice calls can work over 3G/4G/WiFi but quality is definitely unpredictable, and battery usage can suffer. Doing it with SIP2SIM means that the phone has no idea it’s being used as a SIP client, calls just go over GSM in the normal way.

Inbound calls to FreePBX can be forwarded to the SIP2SIM “extension” in the normal way meaning the SIP2SIM extension could be part of a ring group, call queue, conference call …

Outbound calls from the SIP2SIM extension will be routed via your FreePBX trunks in the normal way meaning calls from your mobile phone will be charged at your normal FreePBX rate  (plus a charge for the GSM leg of the call)

The SIM card costs are …

  • £5 one-off setup fee
  • £2 per month for the SIM
  • 2p per min for GSM leg of the call
  • 2p for texts
  • 2p per MB for data

There would also be any costs extension calls would normally incur when calling external numbers. Also, you remember that the SIM has no mobile number so you can’t call it directly, all calls to/from the phone will go through your PBX, just like any other SIP extension. You also can’t send SMS text messages in the normal way.

AA also do a “roaming” SIM which can roam to UK networks other than O2, there are increased costs when roaming but it means you can have coverage when there is no O2 signal. When using the SIP2SIM you can set the network provider name to whatever you like, here’s mine set to SysAdminMan –

AA SIP2SIM in Nexus 5

While using this SIM card could work out more expensive than a normal SIM card with bundle data/minutes the potential for certain types of uses is really interesting. I’m going write more once I’ve tested some more.

5 thoughts on “GSM mobile phone as a FreePBX extension – SIP2SIM

  1. Ruban

    Hi, I have experimented with sip2sim and freepbx. It’s great to have a GSM mobile as extention of pbx. You can add also point a did number to the Sim. There are issue of sms and data which has to be driven by api if you were to use it with third party which is beyond my knowledge. I have tried to set up a mvno but the cost are high for the GSM leg of calls which doesn’t give an edge to compete. Nevertheless this can be put to certain types of use.

  2. Matt Post author

    Hi Ruban

    Thanks for the info and feedback. It’s definitely going to be difficult to compete with the inclusive bundles the main operators can offer, but as a business “extension” there are definitely interesting possibilities such as call recording, PBX voicemail, etc. I was playing with SMS a little yesterday and it’s definitely going to be one of the more difficult areas.

    A&A offer SMS enabled UK geo numbers in some areas and I was able to get SMS working with this. Voice calls to that number can also be delivered to a PBX so that does give the option of a single number for a SIP2SIM device that can be called and receive/send SMS messages, albeit a UK Geo number, rather than a mobile number.


  3. Chris

    Interesting concept.

    Presumably the 2p/min for the “GSM leg” of the call includes the receipt of inbound calls, as well as the standard cost of making an outbound call (which may also incur further charges from the SIP provider)?

    With some SIP providers charging as little as 1.5p/min to call a mobile from a landline, with the receipt of those calls being free, I don’t really see how the charges work in this model. It would work out a (little) cheaper to route an inbound landline call to a standard UK mobile number using one of these SIP providers, rather than routing to the A&A SIP service.

  4. Matt Post author

    Hi Chris

    I’ve been using this for a couple of months now, and it works well. Although admittedly in a dual sim phone, alongside a Three SIM.

    I’m not sure it’s going to save you money in most situations, but there are definitely other benefits for a business phone …

    – all calls are logged through the phone system the same as an extension
    – calls can be recorded
    – single place for voicemails
    – etc …

    Basically all the benefits of using a SIP extension. As you say though you pay for the GSM leg, plus any normal PSTN call charges.

  5. Anonymous

    Good pricing. Over here in Holland all mayor telco’s offer this since 2015. But radio is 6 euro cent to and from your own PBX.

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