You can sync your Google Calendar back and forth with the 3G with three easy steps.
1. Follow my directions below to jailbreak your 3G
2. Download the "Google Apps" in Cydia and then reboot your 3G
3. Download Nemus Sync in Installer
*don't use Nueva Sync -- there is no point to use a third party server that proxies an actual sync. Nemus Sync flows much more smoothly