As others have confirmed, the Treo 700wx does indeed have the tasks function. In fact, it has all of the same components that Outlook has on your desktop, along with the rest of MS Office. But, as someone else also said, you do have to go through ActiveSync to select to sync the individual components.
Be aware, to those that may look at other devices, even at Verizon, they do not all come with the full version of MS Office and Outlook. If you talk to the sales people and read the marketing info, unless you read VERY carefully it does appear that that others come with MS Office but many come with a third party conversion utility called Documents to Go. This has strict limitations that the full MS Office doesn't have.
I've been using PDAs for 7 years now and I would highly recommend taking a look at a program called Pocket Informant, which is a wrap-around add-on info manager and is like putting Mobile Office on steroids! The programming in this software is so thorough, so well done, and so well thought out, that I far prefer using my PDA over my desktop Outlook for info/GTD management. It is HIGHLY customizable with all sorts of groupings, taggings, and so on, that the possibilities are endless. Another set of programs that jack up your PDA are the ones made by SPB Software House. They have the SPB Pocket Plus and SPB Diary programs that enable you to display your info the way you want to on your Today screen, as well as other powerful features. So, the Treo and other PDAs are "good" out of the box, but become "great" when souped up with these programs. This is especially true for us GTD types who tend to want to customize things beyond what most programs allow. The programs above, especially Pocket Informant, are virtually without limits. Microsoft should hire those guys as programmers!
Hope some of this helps. Best, Jay...
PS- I have no interest in either of the companies above but am just a very enthusiastic, long term user. I'm also a computer consultant and have tried MANY programs to make PDAs more efficient.