I am on my second phone. My first was a
Nokia 6160 using ATT. This is a non-flip phone. My current on is a
Samsung T300 which is a half-flip phone (that is the keypad is covered by a flip, but unlike the
N200 the flip does not act as the earpiece).
Anyway, my view is that the flip is so much nicer. Answering phone calls can be so much easier, just open the flip if you set it that way. One drawback to this is, at least with the T300, is that you still have to hit end to ignore the phone call, which involves opening the flip. Also, to terminate anything, by anything I mean a call, a SMS message, 6 levels deep in the menus, all you have to do is close the flip. To lock the keypad, just close the flip.
With the non-flip, you have to set the keyguard. And I was able to turn off the keyguard multiple times when the phone was in my pocket (carpenter style jeans, knee pocket). When the flip is closed on this phone, no buttons work. So you don't have to worry about changing the ringer volume or something like that.
As to recommendations for the Sprint PCS Service. Check
CNet for reviews. They have pratically all the Sprint phones reviewed. And they are fairly accurate. I personally use Verizon and don't like Sprint that much, but you appear to be forced onto Sprint, so I'll try to help you out.