Sorry, I'm a bit late I know but try this:
FishText
There's a free trial and after that you prepay for credit like on a payg phone. The good thing is that the credit doesn't expire. I like it because I use the Java app on my phone in the day so I'm not paying tmob an arm and a leg, but then I use the website at home because it's quicker.
I'm hating all this time limited stuff the networks are doing. Argh!!
