This is happening to me too. Now I am always in doubt as to whether or not I am getting texts from people. If I had anything less than an iPhone I wouldn't have stood for this for 10 min, not receiving texts is really annoying. Just imagine all the people that text you but you don't text them back because you never get it. And then they think you are ignoring them, you know what I mean? It's different than not being to receive calls because people get notified right away when a call won't go through...
similar problem here sending texts to new zealand to family there on iphone3gs which ive had for a week and never recieved replies they are receiving them but i never get the reply , i have tmobile prepay that works fine but so far still not resolved