Anyone know if there is a cheap way to call UK from thailand from a landline?

Depends on where you are calling. UK fixed line, yes. These guys are very cheap. 2 baht/min.

http://www.deedial.com

UK Mobile, unfortunately no. The mobile carriers in the UK charge way too much for termination. Not the Thai carrier's fault. You won't find a reasonable rate until the UK carriers (O2, Vodaphone, etc.) reduce their rates.

These people let you register, top up amount by credit card and only then do they tell you they need a FAX of passport and creditcard. I explained to them that this was not secure or safe, if fact a fax is about the most unsecure/safe way of communications. They were quite rude when I said this and I thus I have cancelled all account with them

I use DeeDial ... U don't need a credit card to topup. In fact I buy my top ups from Family Mart.

Just ask for a SawasdeeCard. Only limitation is its available in 250baht only.