Call routing


Joe asked me about call routing following my post about office VOIP. It’s not a straightforward subject, so I thought it probably deserves a post of its own rather than just a comment reply.

Point of entry – SkypeIn

Having used ‘one number’ for a while in my old banking IT job I wanted to continue in the same way when I left for my new role. SkypeIn seemed to be the only show in town (at the time) that would allow me to have a number that I could redirect where I wanted to. I bought a subscription, which gave me a discount on the number, and also allows me to forward to any UK landline number without running up per minute charges.

Fan out – Ribbit Mobile

Ribbit’s ‘find me’ function lets me have a number of phones ring in the hope that I’ll be near one of them.[1]

Office – SNOM 300

This is a decent SIP phone that allows for multiple SIP subscriptions (four) and has reasonable call handling facilities (hold, transfer etc.)

Home office – GrandStream 286 ATA and Plantronics T20

BT were kind enough to lend me that ATA for testing Ribbit’s SIP functionality. If they ever ask for it back I’ll probably buy a Linksys PAP2T (which a number of my colleagues use for their home extensions). I prefer a headset to a regular phone, and I bought a Plantronics T10 ages ago in order to deal with conference calls whilst working at home. With the extra line that the ATA gives me (in addition to the regular home phone line) I got the T20 so that I could deal with both.[2]

Mobile – BlackBerry 8900

An undocumented (and presumably unsupported) feature of Ribbit Mobile that sometimes works and sometimes doesn’t (and that I wish they would formalise) is that when a call hits its service without CLI from my mobile it knows that the caller didn’t already ring the mobile and so it rings the mobile too.[3]

It’s not actually that simple

Ribbit’s great, but there are times that I need to use Voicehost e.g. to call an office extension. To get my single line ATA to use multiple SIP services I employ SIP Sorcery, where I have a simple Ruby dial plan that routes calls via Ribbit unless I prefix them with 0*.

The people problem

It’s very hard to leave a phone to ring. But it’s also impossible for me to be in my office and home office at the same time, and I spend plenty of time in neither location. This means that when people call me there’s going to be a phone ringing in a place where I’m not, but my family and/or colleague might be. What I want to happen here is for nobody but me to pick up – so I rely on my family and colleagues not to be ‘helpful’.

I could of course spend my life fiddling with the web console for Ribbit turning extensions on and off, but that’s not very convenient


Much better would be if I could have profiles e.g. ‘office’ – just ring the office phone, ‘home’ just ring the home office phone, ‘other’ just ring my mobile. Switching profiles would have to be possible from a mobile (web) app, as it’s the sort of thing that you’re sure to forget as you’re rushing out of the office for a meeting.

Location based automatic profiles

Better still would be if my profile could be automatically switched as I change location – something that my smartphone should already know. There’s not an app for that – yet. Fingers crossed.


Most of my international travel is to the US [4], so I have a US PAYG SIM in an old Nokia 7210 (my last mobile phone that was just a great phone rather than an adequate phone bolted onto a handy little computer).

Most PAYG tariffs (including mine) don’t support conditional call routing, so I don’t get to make use of Ribbit. Here I just use SkypeIn to forward to my US cell number, and upgrade to a global subscription for the duration of my trip so that I don’t get whacked with per minute charges. This means that people can still get me on my ‘UK’ number even when I’m in the US.[5] I also make use of Skype’s excellent ‘To Go‘ service to call home from a US point of presence. I have to top up my PAYG account by $100 each year, and I never in practice use all of that credit, but it’s a lot less than I’d run up in roaming charges if I just used my UK mobile.[6] I also change the call forwarding on my mobile to go to my SkypeIn number, so anybody calling my normal UK mobile gets routed through to my US one.


In addition to the location based routing profiles I’d love it if Ribbit was internationalised so that I could have US ‘purpose’ numbers and route calls to US numbers (as well as UK numbers and SIP end points). It would also be great if I could port numbers between services, which I think is pretty easy in the US, but only seems to work for mobile numbers in the UK.


There’s a video demo of Ribbit Mobile routing that begins with @jobsworth destroying his iPhone (when he was supposed to drop a dummy in the jug of water) – instructional and amusing.

[1] This isn’t how Ribbit Mobile is supposed to be used, at least not without the ‘purpose numbers’ that aren’t yet supported in the UK. The intended usage pattern is for the mobile number to be the point of entry and for the Ribbit service to be connected via conditional call routing.

[2] This hasn’t worked out so well. My T20 seems to have a fault on line 1 which makes the volume really low. Since I bought it from Amazon in the US (as they don’t sell them in the UK where there isn’t much of a market for 2 line home phones) it’s not so easy for me to get service or a refund :(

[3] I’d much rather have an Android phone than a BlackBerry, but when I needed a new phone the only Android on the market was the G1 on T-Mobile (and I was happy with neither). I’m counting the days until I can get an upgrade to something like the HTC Desire or whatever replaces it.

[4] In the past I’ve also run Swiss and Spanish PAYG SIMs, but I don’t spend enough time in those places to keep a SIM active.

[5] Which means that I need to be careful to turn the ringer off if I don’t want an early call from somebody without the faintest clue where I am (and that I’m trying to sleep).

[6] I started doing this after one month where I’d spent two weeks in the US running up £300 ($600 at the time) in roaming calls, and I’m not even one of those people who spends their lives with an ear glued to their phone.

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