O2 and probably other gsm service providers too offer you free text messages through their website. With O2 you get 250 free messages per month, the only pain in the ass is that to use them you need to log on to the site to access the message form. For that reason I only use around 10-15 per month.
That’s no longer the case since I found a neat Italian mobile application called goText which lets me access these free messages from my handset.
Ok, it’s not as seamless as sending normal text messages, they need to do some work on the UI, and of course you have to pay for data transfer but it works and means I can send messages for on average €0.01 as opposed to the normal charge of €0.11 (€0.13 to non-O2, €0.25 international!!)! That’s a heck of a big saving even if you only send a small number of text messages.
GoText works with O2 and a number of other service providers throughout the world but I have no idea if it can be used with Vodafone, Meteor or others here. Check out their configuration page for a list of service providers and their page on GetJar for a list of compatible devices (but download it from the goText homepage for latest version).
p.s. I should mention that for those of you who can’t use goText there are a number of alternatives such as smsBug which will cost you €0.03 (plus data transfer) per text. Check out GetJar for other options.
Are you telling me that you have read the instructions on those pages in Italian? WOW, you are a genius!
Italian is such an easy language
) No, I wish, thankfully they have an English translation! 
Of course, I found the translation buttons much later
at least I was a genius for a few minutes