I heard that if u have the 02 sim card that offers 300 free texts & wap minutes, you can keep getting 300 free texts every month without 'topping-up'. Once you run out of free texts, you change the phones date back to the date you initially topped-up, don't text for that whole day, the following day you can correct the date & you should have another 300 free texts. Don't know if it works though. Other than that, you can purchase cheap texts on the 02 site u currently use.
The dates are still kept at o2's end, so how that's going to work is beyond me. It's like changing the date on your answerphone to get out of paying your phone bill.
www.mobilepda.com does free texts, you get 5 or ten a day + about 50 to start and you can earn loads by doing little questionares and stuff, you can also earn mobile phone logo's, ringtones design and send your own logo's- all for free !