One possibility for GTD on webOS is Outline Tracker (http://outlinetracker.com/outlinetracker/index.html)
It syncs with Basecamp (http://basecamphq.com/) rather than Outlook.
If you have outlines in Natara Bonsai, CodeJedi ShadowPlan or Ultrasoft BrainForest, you can export them and import them into Outline Tracker: http://outlinetracker.com/outlinetracker/migration.html
Under webOS 2.0 (currently on the Pre 2, and coming to older devices in the next month or two) you can create new items from Just Type (universal search). This requires Outline Tracker 2.0, which should be released this week.