The T-mobile sidekick (a.k.a. Danger Hiptop) is a text pager (via email or IM), phone, and has limited PIM features (calendar, to-do, etc.). HOWEVER, it is not really a PDA, in the sense that you cannot add any software to it, you cannot create any kind of documents with it.
if only we could merge the text pager bit with the pda bit, i would be so happy! alas. (blackberry devices have this problem too -- great pager/email access, but not good as a laptop/notebook replacement that can handle software, documents, etc.) i will probably get a separate text pager and separate pda. Still leaning toward a PDA with the largest screen and best screen resolution (VGA would be nice).