It's a good idea! I've spent many, many hours and lots of money trying to find the perfect combination that gives me what I already had with two devices -- phone plus PDA. Here are mine so far, and the one I wish I could have:
Agendus Pro: I need to carry my calendar and contact database with me. The contacts number 6,000+ and growing. The calendar changes daily, but my career depends on it. I also have other ad hoc things to track. So I download the work calendar and contacts to my Treo 650 each work day, then add a few personal events or tasks for that same night or the next day. With Agendus I can highlight certain things with color, icons, etc, so I can quickly distinguish things on a busy day. Also, I can show things as having been done with strikeouts, etc. There's much more, but those are the essentials.
Butler: It's my alarm clock every day and it is amazing. Lots of flexibility and I am never late. It does other stuff, too, but the alarm clock is the main thing for me.
Brainforest: I don't use this a lot, but occasionally I have a desperate need for an outlining program for my work and this is the perfect tool. Especially when I don't have pen and paper with me.
SmartList: A++ database. I use this for numerous things like tracking time and mileage, Christmas lists, and other things. A Very flexible and easily programmable database program for Palm.
TMTraveler: As a Boy Scout leader, TMTraveler lets me carry my entire Troop database, including the boys' emergency contact information and medical emergency information, into the woods. When a boy falls into a ditch you need three things: a long rope, the skill to tie a bowline knot, and his Mom's phone number!
Passwords Plus: Because I can't keep up with all this stuff, and this lets me do it securely with my PDA.
PrefDoctor: Save preferences during reset (even unintentional reset) so I don't have to redo everything a million times over. God I love this one!
Phone Technician: It does a lot of great things. But mainly, it boosts the sound so I can hear the other party on my phone calls. Gotta have it.
Backup Man: An absolute must have program. It does automatic backups on my schedule to my SD card so I can mess something up and later recover the correct stuff.
PDAReach: People wonder why this is important. I can drop my phone in the cradle at home or at work, turn this program on, and manage most of my Treo's programs and functions from my laptop or desktop computer. It just makes life so easy.
Bike or Die: Because you need to have a game, and this is the one I like. Addictive, challenging, competitive.
PowerRUN: I place this one last because it's the one that permits all the others. It lets you easily move certain programs onto the SD card so you won't run out of RAM and drive your Treo into an endless loop of resets.
Now, I wish I had . . .A good program that would function like CallFilter and work with my Treo 650 system with a very large (6,000+ entries) contact database. Something that would let me block unwanted calls, send calls directly to voicemail without ringing while letting certain people ring through, etc.
This setup works for me on a Cingular Treo 650. I experience few resets, and when there is a reset I do not lose preferences. The device comes back just as I left it.
Hope this helps,
Greg