I thought I should share this as we're the type of people often in low mobile phone signal areas.

http://www.emergencysms.org.uk/

And the leaflet for download is here: http://www.emergencysms.org.uk/files/3649_esms_6.pdf

What is emergencySMS?

If you cannot make voice calls, you can now contact the 999
emergency services by SMS text from your mobile phone.
Emergency SMS is part of the standard 999 service which
has been designed specifically for people with hearing loss
or difficulty with speech

I mention this because there may be time when you can send a text because you can just about pickup phone signal for odd seconds (enough time for a text to be sent) but wouldn't manage a voice call. I only found out about this today...

Not heard of this but somebody told me some time ago that 999 calls will search for, and use, another network if a signal can't be found on your own network. No idea of the details though.

the important bit on this is you have to register your number before you use it - otherwise no worky