Came here to post something similar. I've been with Sprint for years and have experienced these problems. To be fair though, it happens very very rarely (as far as I know).Yes it's common, and the only way to resolve it is to take your Sprint iPhone 4S back to the Apple store and exchange it for an AT&T or Verizon model.
Texting delays on Sprint are par for the course, regardless of what phone you're using:
They use a messaging system that's - to use a polite term - "highly customized." The end result is that it's difficult to troubleshoot when there are issues, and the engineering staff don't particularly enjoy doing it so it's often put off until it can't be avoided. And so there are frequent, lengthy periods where systemically, text messages are queued in their network for hours, sometimes even days before they are delivered. And that's on-network. Woe be to you if you try to text someone who's not on Sprint, or they try to send you something.
The only other option is to get all your friends to use iOS devices, and send them iMessages, which bypass Sprint's text messaging system as long as the recipient is connected to a data network.