From The Official Palm Blog:

Unlocked GSM Palm Treo 680 smartphone customers - there is a new software update that is available for download here. The software update includes these features:

• Corporate email as it arrives - Have your corporate email delivered to you with Microsoft Direct Push Technology.
• Power saving enhancements - Helps conserve battery life with improved power management and updated default system power preferences.
• Supports larger expansion cards - Supports up to 4GB SD expansion cards (including the SDHC format), sold separately.
• Enhanced ringtone support - MP3 and other sound files purchased from the web or sent from friends can now be set as ringtones and alerts (formats: MP3, AAC, AAC+, MIDI, WAV, and AMR).
• Three updates in one - This update incorporates three previously released software updates: Treo 680 Camera Update (January 2007), Treo 680 Security Patch (May 2007), and Treo 680 Unlocked GSM Smartphone SMS Update (July 2007).

For additional details and to install to your device, visit the Palm Treo 680 product support page.

Source: The Official Palm Blog