Please Note: The free SyncML LITE provides contacts sync. If you are looking for calendar sync, please check out SyncML PRO (synchronisation of built-in iPhone calendar on iOS 4) or Todo+Cal+Sync (with separate, full featured calendar and task manager).
SyncML LITE for iOS brings SyncML standard based data synchronisation to iOS devices.
This allows mobile over-the-air (OTA) data synchronisation with any compliant SyncML server (such as Oracle Calendar and Beehive, goosync.com, consolidate.at, Open-Xchange, MDaemon, eGroupware, Winfonie and many more).
The Built-in SyncML server allows direct phone-to-phone sync over Wi-Fi - not only with iPhones but with any other SyncML and Wi-Fi enabled mobile phone or computer as well. See support link for documentation.