SyncContact synchronizes iPhone with contacts or contact lists on other systems.

- Microsoft's SharePoint Server 

- Google Contacts

- Yahoo AddressBook

Note: SyncContact works one-way i.e. pulls the contacts or contact updates from the source and adds/updates iPhone contacts respectively.

Once synchronized, all the contacts from the configured sources would appear in iPhone contacts. iPhone Mail Application suggests and auto-completes email addresses, so no more recalling of Share Point/Google/Yahoo contacts when sending a mail.

iPhone would have to be on VPN if SharePoint server is behind the corporate firewall or within private network. 

iPhone doesn't allow applications to run in background, synchronization happens only when SyncContact is launched and requested to synchronize i.e. by hitting/pressing 'Sync' button.