Both phones are made by HTC.
Here's the lineage:
HTC Tanger = qtek 7070 / Orange SPV e100
HTC Voyager = qtek 8080 / Orange SPV e200
HTC Typhoon = qtek 8010 / Orange C500 / Audiovox SMT5600 / imate SP3
So basically, the SMT5600 is a generation/model newer than the SMT5600. Huge size and battery life difference.
Despite the fact that it has a full SD card, I don't think you'll find many people that will recommend the 8080 over the SMT5600. The 8080 is pretty rare to find in the US. You might want to check out the forums over at
www.MoDaCo.com and look for SPV e200 / C500 comparisons. They've had both phones for quite awhile now.
FWIW, you can get a SMT5600 for something like $350 from Amazon without an AT&T contract, -$25.01 with an AT&T contract. It's still SIM-locked to AT&T with public way of unlocking, but that's being worked on.
If you don't want to deal w/ unlocking, etc, the imate SP3 should be out shortly. It's SIM unlocked, but in the $450 range.