Depending on what you'd like to do, a smartphone may be the perfect square peg for your round hole.
> for remotely administering Linux/UNIX boxes via SSH
What does remotely administering mean for you?
Lightweight (examples, not exhaustive)
* Killing/restarting processes when the pager goes off
* Acknowledging alerts/pages from your monitoring system
* Minor troubleshooting in a jam
* Simple edits to a config file before a kill/restart
Not-so-lightweight
* Involved troubleshooting
* Large-scale edits
* Many user, system, filesystem modifications at once
Heavyweight
* Postmortem analysis
* Adding users, filesystems
* Creating/Developing anything
* Day-to-day administration tasks
If you're doing only lightweight (and maybe some not-so-lightweight) activities say when you're on call and don't want to drive home from the movie/dinner/play/bar/club then most any smartphone with most any keyboard will meet your needs. Will your frustration level rise as task complexity rises, YES. But this should only be an occasional thing. If you need this regularly then you need to stabilize your infrastructure... or choose another career where your skills are stronger. If it's going to be needed frequently in the short term (while say waiting on a vendor fix) then optimize for remote use while at your desk with some aliases or scripts.
If you're wanting fire up a full screen editor (vi, emacs) then you're moving into heavyweight tasks and/or wasting time massaging your editor bias ego. Get over it, stop whining, and learn ed. It was designed for an even more limited environment than your smartphone and works everywhere. Sorry, subshells not included. You can find your favorite metakeys when you get back to your desk.
If you're doing heavy stuff, use heavy equipment, that's what it was designed for. You don't move pallets with a spatula, you use a forklift. Maybe try a small laptop and cellular data, it's the happy medium pallet-jack equivalent.
I've used a regular palm, 3 different treos, and even a samsung a900. They all got the job done. Today I use an iPhone and webshell. Webshell isn't the simplest client to set up and has its issues. But, it also has a ton of flexibility with multiple virtual keyboards and has added some pretty cool gesture support. It's the least frustrating of all the solutions I've used over the years.
Don't forget to live while you're wandering the world smartphone in hand, reading 8 different email accounts, all the very fulfilling blogs, and loading your favorite emacs extension while rescuing your company's web site. There are some pretty cool other things like outside, physical activity, girls/boys, vice & stuff.... smartphone not required.