Sorry for double dipping on the threads but my iPhone lags with my text messages randomly. Sometimes it is right after I use the net and other times its when for seemingly no reason at all. When I say lagging I mean I press buttons and make sentences and the letters lag behind being pressed.
Both mine and my girlfriends phone have it really bad. Not just typing either. Switching applications and/or scrolling as well as all areas of the phone application (i.e. phone book, recents, etc...). Lag all the time in all those areas.
this happens to me quite often, usually what I do is press the home button repeatedly, usually three times in quick succession, then go back to text. works everytime.