Buy a telephone card from the supermarket to use in a call box they are cheap enough ,good value and you can have a good natter .Only use mobile for emergencies.
I am on O2 pay and go and pay £10 a month and get 300 free texts or 100 picture messages. However I have noticed over the last few years if I send a text it costs me 49p however if I send a picture message (which can have a lot more characters is) doesn't seem to cost me at all it just comes off my 100 picture message allowance. If you do pay I think if my memory is right is only 25p.
Usually use a phone card though to phone as this is much cheaper.