I am an iPhone noob. I've always used a Palm phone but I've finally decided to join the iPhone world when iOS 4 was launched. The first thing I did when we got the phones was to jailbreak mine. I did his after 30 days because I don't want to mess up his phone. Everything went smoothly, no issues and I am truly happy. So, last night, when I was syncing our phones with iTunes, something terrible happened. I synced his phone, signed-in his gmail account. When it was done, all his 375 contacts were wiped out to be replaced with mine. I have never been this scared in my life. His phone is his work! I really don't understand why this happened (we shared 2 phones and an iPod touch on 1 iTunes). So, I panicked and did a restore on iTunes without reading the restore instruction here on MacRumors. Well, it ended up upgrading the iOS to 4.1 from 4.0.1 and lost the jailbreak 
but he got all his contacts back. So, 2 questions: 1) How safe can I jailbreak his phone again? 2)Will a regular sync back-up all his contacts without going through Gmail? Never want to touch that "Sync Contact" section again.
On a side note, I have been reading MacRumors ever since we got our phones. I have learned so much about the iPhone and especially about jailbreaking. Thank you all so much for your advise (& the laughs) and for sharing your knowledge to noobs like me.
but he got all his contacts back. So, 2 questions: 1) How safe can I jailbreak his phone again? 2)Will a regular sync back-up all his contacts without going through Gmail? Never want to touch that "Sync Contact" section again. On a side note, I have been reading MacRumors ever since we got our phones. I have learned so much about the iPhone and especially about jailbreaking. Thank you all so much for your advise (& the laughs) and for sharing your knowledge to noobs like me.