There's two tricks I can think of for receiving other people's messages:
1) You need to use spyware that you can download onto their phone. You can get them to download it themselves by sending it in through another application (such as a game)
2) If they're using iPhone, take out their SIM, put it in your iPhone, sync up with iMessenger on your laptop, and then return it to them.
I've been doing this and receive messages from another phone direct to my laptop.
I should point out though, that hacking someone's phone without their permission is illegal and you can end up in serious trouble - so overall, I don't recommend it.
What do you need it for anyway?
