Note: The information here is not new. However, from reading forums, etc., it seems as though that a lot of people still aren’t informed as to the best way to utilize Gmail/gCal with the iPhone.
If you don’t use Exchange with your iPhone and want cloud-based email and calendaring, Apple’s solution is MobileMe. Known startup problems notwithstanding, there’s nothing really wrong with MobileMe if you don’t mind paying $100/year. However, if all you need out of MobileMe are email and calendar syncing between your desktop, iPhone, and a web client, then Gmail and gCal already have it covered.