Just noticed this so don't shoot me down if it's old news but do you know that if you are a 18185 user (www.18185.co.uk) you can text as many messages as you like for 1p per text?
As a customer of 18185 you can send very cheap text messages. Log in with your (mobile) number and your 18185 customer number and you can send text messages right away via the internet. The sent messages will be charged on your regular invoice automatically.
Send text messages to a mobile phone to any country from only 1 pence per message!
You can also make cheaper calls from your mobile too.
A 4pence connection and then 3.5 pence per minute to other mobiles.