Stryfox,
I am a Cingular customer and I have, what I belive to be, my best cell phone yet. It is the Audiovox SMT-5600:check out a review and video on it here.
http://reviews.cnet.com/Audiovox_SMT560 ... 38516.html
This phone sounds great, has great reception, is small and light (candy bar form factor) and has a ton of extra features like a built in mp3 player,camera, Windows mobile etc. I know you said you don't need anything flashy, but you get a lot of "phone" for the money.
Also, I have talked with both Pioneer and Audiovox and I'm told this phone is definitely compatible with the Z1.
Cingular has since released their own version of this phone the Cingular 2125 (due to the 5600's immense popularity), and it may be difficult to get the original Audiovox version...usually you can find it on eBay for under $200.
You can always go with Cingulars version :
http://onlinestorez.cingular.com/cell-p ... WT.svl=img
I know this may be way more phone than you're looking for, but this IS one great phone AND as I said it is supposed to work just fine with the Z1.
Hope this helps.
Rob