I have been thinking real hard about this for a long time.
I am on Sprint, and I can get a Centro smart phone for next to nothing and it won't change my cash outlay very much. I would love this for looking at the traffic situation in Minneapolis over the web. The problem is it's a Palm system. Not a big deal because it will sync with my mac nicely minus any GTD usage. Not perfect, but a low cost. On the other hand Palm looks dead compared to what Apple is doing with PDAs.
I am using The Things GTD application for Mac. I am sick of analyzing GTD software and am pretty satisfied with it for my purposes. Things will be able to sync with iPhone and iTouch later this summer. An iPhone is much, much more expensive and I need to figure out if that's worth it for the ideal GTD set up. I will so minimally utilize the other features of an iPhone so it really gives me pause. I am not a heavy cell phone user. An itouch is o.k. but you lose the internet in a big way compared to iPhone or Centro.
Centro = $100 + 45/month
iPhone = $500 + 60/month
By my analysis you will be $1000 poorer over three years with the iPhone. The question is, is that worth it? It would just be incredibly nice to see the traffic and have a super GTD app in one perfect gadget.
An itouch with limited web access and needing to carry a cell phone anyway seems so not that great. I don't know what I'm going to do.
(since Sprint is having so many problems I wonder if I can get that lowered, too.)