The V186 is simply a V180 with EDGE. It doesn't have any special features to take advantage of the speed, though. It's mostly designed to be used with a laptop via a USB cable.
The V171 (on the right above) is a new entry-level GSM phone. "Entry-level" might be generous, though, because the V180 was entry-level, and this is one step below that. It seems that carriers wanted something even cheaper, so they could continue to offer freebie phones without cutting so deep into profits. Thus the V171 was born.
So the V171 has a very small main display (although it is color) and no external display.
The E375 is a stylish new bar-style phone. It's intended only for Asia, but it is tri-band GSM. It sports a large 176 x 200 display and a VGA camera with LED flash. Otherwise it's pretty basic.
The C698p is a PTT (push-to-talk) version of the E398. It's designed to be a mid-tier phone, though, so it doesn't have all the features of the E398. Features like Bluetooth, haptics, and MP3 player are not present, to lower cost. It's currently targeted at Latin America.
The C381p is a more basic entry-level PTT phone. It's basically the C380, but to accommodate PTT, there's an extra speaker on the back, and a dedicated PTT button above the talk button.