Tech: Managing calls

I have just issued a new alpha release of FireBrick, by popular demand, allowing some call filtering based on CLI. Basically you can do a lot more than simple anonymous call reject now. Whilst most people know the FireBrick as a firewall/router it is also a SIP VoIP PABX (phone system).

But one of the things that this highlights is the increasing need to "do something" with calls you receive. Systems like the FireBrick allow you to do all sorts on your own network, making your own "phone system" for VoIP phones. If you look at systems like asterisk the level of controls you have are quite incredible - essentially a programming language for how calls are handled and even allowing recoded messages and DTMF menus and so on.

On a private system you also have means to log things and even manage call recordings yourself.

This is all great for a "desk phone" but what about your mobile?

This is where some of the stuff we sell comes in - and we have customers doing some clever stuff. Recently we have managed to make a few improvements, but basically we have means to have a normal 07 UK mobile number, and a mobile SIM, and put your own phone system (whether FireBrick, or asterisk, or anything else) in the middle.

This means you can have a mobile phone with a SIM card, and do things like log, or filter, or record calls, and texts, either way. The SIP2SIM service looks like a VoIP handset has registered and connected to your phone system, but is in fact a normal Mobile telephone service (i.e. no special app on the phone). This means you can even make internal calls on your phone system from your mobile. (The mobile leg does have call costs even for these).

The texts can be passed by email or using http/https on your own server where you can do things with them. The latest improvements mean much better handling of unicode characters as well. You can also handle the texts from the mobile. You could just join the dots to make texts or calls, in and out, like a normal mobile, or you could do much more with your own scripts on the way.

We have people doing things like opening doors using calls, and clever tricks with texts.

Obviously we also have services that simply link calls, or texts, or both, in and out between an 07 mobile number and the SIP2SIM service without needing your own phone system. We have options like call recording and logging. But we are happy for you to make your own systems, as simple or as complex, as you wish in the middle.

Of course this also allows mobile on a normal landline style number, but texting to such numbers remains a challenge in the UK, and a lot of companies and web sites will refuse to even try texting what they think is a landline number. So using a normal 07 mobile number does the trick nicely.

We can even port in an 07 mobile number to the service, and if you don't like it, port back out again. No minimum term on the SIP2SIM or VoIP services.

So if you are techie, but want a lot more control of your mobile phone service, it is worth taking a look.

One little trick I do a lot is steal a call, transferring it between my mobile and my desk phone mid call, without the other party even realising I have done it. E.g. answer on mobile, walk to desk, put on headset, switch call to desk phone and work on computer while on the call. All seamless.


  1. I use the service to put a call gate on my mobile number.
    Ported my Mobile number to A&A.
    Pointed it to Asterisk.
    Call gate.. If real human then transfer call to my actual mobile phone.

    And, as you say, Also gives the great function of being able to jump the call over to my desk phone when I get back to my desk! (better call quality).

  2. Fun fact: the show from the number that you've used there must have some fans in the Android developer community, because when you try dialling it on an Android phone it buzzes when you get to the end...!

  3. I love the idea of the SIP2SIM service (and especially the easy ability to get network recording of mobile calls, which would be extremely helpful for my business), but for the crazy data pricing.

    £17.50+VAT per GB of mobile data makes it impossible for me to consider using this service for anything other than very specialist situations (e.g. I have one in the GSM module of the gate controller at my house).

    How can someone like GiffGaff do unlimited calls, unlimited texts, and 10GB of data per month all for £10+VAT? Are their underlying costs really so radically different?

    1. I find that I am using wifi so much these days (shops, home, office) that it is not an issue. But yes, it would be good if we can get those prices down.

    2. Yep, we've finally given up on SIP2SIM on our main phones due to data pricing.

  4. > Are [GiffGaff's] underlying costs really so radically different?

    The subsidiary of O2 with ~£450m revenue and ~3m users? Yes, its costs will be radically different!

  5. Any chance of offering your SIMs on the EE network rather than (I recall) on O2? And also at a more realistic price as mgboyes requests. Even though I use WiFi most of the time, I still get through about 5 GB a month of mobile data.

  6. Another +1 on data pricing, we use sip2sim in dual sim phones with data disabled and use Vodafone for data - would like to use just sip2sim though.

    Would data packs be possible? Buy set amount of data each month eg. 2GB and cut off when runs out or allow data to continue at cost? Thanks

  7. Off topic, but any chance of getting the Firebrick to do DoH / DoT so you only need to configure the brick and not all the devices?

  8. +1 ... A revised offering for SIP2SIM data pricing would allow me to take it as my main service rather than having a SIM that I forward the calls to :)

  9. We would probably have used SIP2SIM if it wasn't for the absurd data pricing - instead we've gone with a 3CX system which seems to work pretty well over mobile data/wifi/etc. We did consider the Firebrick's PBX features with some of our customers but there's just too many missing features for it to be viable - instead gone with FreePBX, 3CX and sometimes just raw Asterisk!

  10. I use the Sip2sim service in a Nokia without data. Works great, roams to any network so it’s rare to be out if service but for data I use three, not as good as they were and still don’t support Apple Watch, but as I typically use 200gb of data it’s the cheapest about at £20 a month.

  11. A&A's pricing largely reflects the costs to them and they do things differently, like SIP2SIM, so a few aspects may be disproportionally high compared to mainstream offerings. A suggestion for some of the commenters above: to get the benefit of SIP2SIM and a better data price use a dual SIM phone and set one to be the default for data, the other for phone.

    1. Interesting, I wasn't aware that was an option with dual SIM phones these days. Assumed they were still like the older models where you could only have one SIM active at a time.

  12. Any chance of an eSIM for SIP2SIM? My phone allows SIM+eSIM but not two SIMs.

  13. Any news on eSIM for SIP2SIM? Thanks


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