How to sync Gmail contacts keeping exchange contacts?
Use iTunes to sync and make sure you have your phone contacts in your MS-Exchange folder. Then you can either use the Google Apps migration tool or export them from outlook and into gmail.

Next you can remove the exchange account (which will probably delete you contacts).

Next you can uncheck the box in itunes that says "sync my contacts" so that they will all come off of your phone. Make sure you have them backed up first.

You can also uncheck the box to tell it not to sync the calendar if you like.

Next, you can add a Gmail account or google apps account - but when you do, don't click on Gmail for the account type - choose "Exchange" because it allows syncing of contacts and calendars, too.



See the gmail site for more details:

http://www.google.com/support/mobile/bin/answer.py?answer=138740