Apologies for incorrect information and thanks to df for pointing out the various plans that I hadn't kept up with.
I use the phone very little relying, instead, on VOIP. My provider offers 'free' (=included) calls to Thai numbers, fixed and mobile, from anywhere I have a computer. Similarly to US, fixed and mobile and UK fixed. For anyone needing to phone Thailand every day, it's a boon.
Voip