I have am using a 3G iPhone with firmware 2.2.1 and it is Jailbroken. Whenever I connect to other iTunes, that aren't the computer I use to load music onto my phone, I can't play music from my iPhone. Is this a general issue or is there something wrong with my iPhone?

My iPhone was original done on an old laptop, and that laptop crashed, and I had to reinstall everything. I used TuneAid to pull all my music off my phone, then manually sync it to that same old laptop. I have tried 4 other computer and not of them with let me play any music from my iPhone.

If this is a general issue with iPhone, I would hope there is some way around it, because that is super annoying.