Just purchased T600 yesterday. Installed Sprint 1.20 update today as per instructions at palmone.com. Installed flawlessly. Works flawlessly as well (so far).

Running Mac OS X 10.3.4. Syncs perfectly and fast with Palm Desktop 4.1 and iSync (1.4) for Contacts and Now Up To Date (4.5.2) for Dates and To-Do's.

Set up mail on Treo as well. Loving it a lot.