I spent ages looking at trackers for dogs and landed up getting one of these:
http://www.traccauk.com/tracca-dog/
A lot of the trackers will only use 3g data services but the Tracca one also works on 2g and also without a data signal at all.
There’s an app for the tracca collar but you can also just call the mobile number and it will text you back the map coordinates in a format that google maps uses. The battery life is extremely good – the only downside is that the GPs unit needs to be zip tied into the rubber mount as it can pop out if the dog runs through undergrowth.
I used a sim from anywhere sim that roams across the uk networks – so far we haven’t found anywhere it could t get a signal on one network – the £60 a year pre paid “annual sim
Lite” sim has more than enough texts and data included (our dog runs off – – lot!).
http://anywheresim.com/buy/#anywhere-sims