The LG PM-225 had the worst battery life of any phone I've ever used and the FOTA (firmware over the air) function never worked like it should have. Also the Kyocera 2255 had the problem where lint would get trapped under the LCD screen.
I have not heard more complaints about any phone other than the LG 225 and the CDM 120. Unfortunately, because of their cheap (read "free") price, they sell like hotcakes! I think these phones might be half the reason people think that Sprint has a bad network!
I have been in this game for a while, first in sales, now on the network side. here is my list of absolutely horrid phones in no particular order
LG 1010, Samsung A460, Moto V60v, Samsung A640, sansung N240, and the absolute worst, was the Samsung N400. I was also not impressed with the Treo 700p, but that is a software issue, the phone itself worked great.
I have always loved my samsung phones, when I sold phones I wouldnt sell any other type of phone. I actually have a real story I told customers about samsung. Anyway the worst phone I have ever owned was a motorola, it has been awhile so they have probably gotten better, hopefully right.
There was one phone, I believe it was the LG 1010 or 1200 that had a widespread problem of the phone going into a state where it would constantly shut off or power cycle. The Samsung N400 probably had the most bugs out of any phone ever.
No doubt in my mind the N400 (samsung) was and is the worst phone ever made from sprint. Design wise it was a neat phone. But there were so many bugs and problems. My SCP 7300/RL 7300 did not have one issue like the N400. And reception was 100x better ! Whew.