If your worried about losing your contacts etc etc, then just run a full back up before jailbreaking.
When I have JB my phone and others, the iTunes music was never deleted from the iPhone, neither was any of the photos, contacts, messages etc. The phone was just in the same state as it was before. But if you are still worried, then to your question, yes, as long as you have a recent backup & also your music is in your Library, then you can sync once jailbroken to load everything back on, but I highly doubt you'll lose stuff when JB.
Tbh, Jailbreaking is the EASIEST hack known to man, aslong as you locate the right QuickPwn for your firmware, its a case of loading up the QuickPwn, and following the on screen instructions.
i.e
1. Make sure your phone is connected
2. Click Next
3. Hold the home button for 5 seconds
4. Hold home and power button for 20 seconds
5. Let go of the power button and hold home for 10 seconds
6. Let go of all buttons
7. Click next
8. Job done
If you dont think you can do that, then i'd be worried.
