http://www.fishtext.com/ » and it provides international texts from just over 1p and UK texts for 2p. There will be a small data charge from your network provider which will vary depending on your data charges.
So far this is the cheapest and most reliable service i have found. I've looked at other possibilities such as smsbug or mobiwireless but they just don't seem as good.
Please add to the thread if you know of any other services like this
someone else did it the same night but they didnt I dont recall who it was though