Remember the Milk?
 

Stumbled upon a competitor --

[url]http://rememberthemilk.com/[/url]

it has an iPhone interface via Safari at

[url]http://i.rememberthemilk.com/[/url] (for $25/year though)

Didn't find many needed pieces there though -- syncs only given "lists" to iCal, has lists and tags, which you can use to implement contexts, and other mismatches with the GTD as we used to know it. Anyways -- for those who used RT[no F!]M, what's folks' impressions?

Apparently it syncs the todos to iCal via webcal://, which is useful -- that's how I found it, trying to sync my Zimbra todo's to something Mac'y/iPhone'y.