Official Bitcoin client cannot run on ARM due to wxWidget GUI
Ram is not a problem. I can run bitcoind even on Nokia N900 (ARM Cortex-A8)
I think bitcoind is "official", and it is a fully working client, I have never used the GUI version.
256 MB (as in the N900) is enough for bitcoind, but not very good for extended use IMHO. I have one running on a 256 MB ARM server, and it uses about 400 MB of virtual memory. I used to have a 128 MB ARM server as well, and while it could run bitcoind, it used to swap a lot. I also have a feeling that bitcoind was somewhat leaner at the time (about a year ago).
Command line use on a smaller device is harder, but the main problem is entering the address, which you need in a GUI as well. Of course, you can use copy/paste in both kinds of client.