Palm is now offering a Windows Mobile 6 update to AT&T customers with Treo 750 smartphones, and this week also began selling an unlocked version of the phone.

The Treo 750 is a five-band smartphone that works worldwide and combines e-mail, messaging, Web browsing, and organization software. It has been shipping with Microsoft's Windows Mobile 5 operating system for some time, but the Windows Mobile 6 update will give Treo 750 users additional capabilities that were lacking in the previous version.

One of the major enhancements is faster access to large attachments, streaming video, and other bandwidth-hungry content and files. The update provides support for High-Speed Downlink Packet Access, a third-generation cellular technology, which AT&T claims offers download speeds of 600 Kbps to 1,400 Kbps.

With the update, Treo 750 users also get the ability to send and receive e-mails formatted in HTML with tables, bullets, and colored text--just like they were originally created on a desktop.

Other enhancements include the ability to remotely wipe the smartphone and SD cards clean if they're lost or stolen, the ability to synch the Treo 750 to a Windows Vista PC via Microsoft's Windows Mobile Device Center, and direct "push" technology that delivers e-mails to the phone straight from Microsoft Exchange Servers.

The update is available as a free download on Palm's Web site.

Also this week, Palm began selling the unlocked version of the Treo 750 online and in its retail stores. The smartphone doesn't need to be updated since it already comes with Windows Mobile 6 built-in.

While previously offered in the U.S. only through AT&T, now the Treo 750 is available to a broader group of mobile users. However, since the smartphone uses cellular technology based on GSM, it's not compatible with services offered by Verizon Wireless and Sprint in the U.S. Both carriers use a technology called CDMA.

The unlocked Treo 750 costs $549.