Without a doubt, the best service/phone combination I've ever seen and used, including UI and phone design/features, is Sprint/Samsung.
First, Sprint's calls are the clearest and cleanest of all providers. No doubt, they're a bit more expensive then the rest, but I'm really happy with my plan right now. (800 anytime minutes, 5200 night and weekend, 2 meg internet access for 59.99.)
One thing that I REALLY like about Sprint that I CANNOT STAND about anyone else is that if you're out of range or for some reason your phone can't be contacted, Sprint will automatically bring the caller to voice mail. It sounds like common sense, right? Then how come Cingular and Verizon and AT&T and the others haven't figured that shit out? The others, after forty seconds of ringing at times, just tell you that the caller can't be reached; try again later. GOD that is so annoying. And then when you finally get to their voicemail prompt, you have to listen to the Operator tell you they're not there, if you like to leave a message, hold on some more, or, if you like, press 1 to disconnect..... Press 1 to disconnect?? WTF?! If I wanted to disconnect, I'd ****ing hang up! Then you have to listen to the actual message and THEN some services make you listen to the operator again! WHY?!!?!?!?!? With Sprint, let's say you call me, you hear this: *ring* "Hey, leave a message." Beep. No time wasted, no needless time spent on the phone racking up minutes on your own cell phone! The way it should be!
As far as the Samsung phone goes, it's beautiful, y'all should check it out. I always buy Samsung for my phones. Voice record, Calander, Sheduling, Alarms, multiple phone entries per person, fast UI, amazing graphics, cool animations, one touch dialing, voice dialing, digit dialing (where you speak the numbers and the phone dials it for you), email access (to your Sprint account as well as pop accounts), downloadable games and ringers and screensavers and applications, web access and tons more make this phone simply amazing. Most of these features (like voice and one touch dialing, multiple entries per person, email access, fast UI, calander and scheduling, etc) have been standard for years.
What I love about the A500, another awesome feature that Samsung has had for years, is the tiny flip phone enclosure. This is good because it keeps the size small while protecting the main screen, but there's a smaller screen on the outside that shows you time, date, caller ID information, as well as signal strength, voice mail, and battery power. Very cool phone. For anyone interested, I'll include a link.
And to top it off, Sprint's services, while a bit more expensive then the others (though nowhere near as expensive as GPRS) is really top notch and widely available.
Be back with the link.