I tried both that motorola (a845?) and the Nokia 6651. They were both pretty terrible in a number of ways. In the end the Merlin UMTS 1900 card was the best reasonable option for actually using UMTS data.
The Motorola a845 was easily the worst phone I ever owned and I have owned quite a few phones. It was very unstable and crashed a lot. Most of the time when it crashed it would still be consuming power at a pretty good rate, the screen would be black, it wouldn't receive calls, and I'd need to remove the battery to get it going again. This would happen at least once a day. I returned the first A845 I bought figuring it must be defective, tried a second and it had exactly the same problems. It would also drop calls more or less constantly, either in GSM mode or UMTS mode, and incoming calls would often end up with a fast busy (was that the phone, the network, a combination? who knows). It would also drop data connections. No EDGE, so it was either GPRS (very slow) or UMTS (nice and fast).
The Nokia 6651 was better. No GSM 850 (but it could hold a call on GSM better than the Moto, go figure). It couldn't effectively tether on Bluetooth because of a speed limitation on Bluetooth transfers. USB was the only way to go for tethering, and that mostly worked. It was actually pretty stable, with good sound quality, but also pretty featureless. Again, no EDGE, but it would fall back to GPRS. Lack of GSM 850 and the Bluetooth tethering issues were the main issues.
The Merlin card was UMTS 1900 only. Wouldn't do EDGE or GPRS, but the thing actually worked quite well. Being an early adopter of UMTS was troublesome, but the speed was really worth the pain.
How AT&T Wireless managed to qualify the A845 for anything, I don't know. The only thing it was really good at was being a paperweight, being so big and heavy.
Didn't really mean to hijack the thread though. Nice that the E61 VOIP issues are better. I've actually had reasonable luck with Truphone over WiFi even with the v2 firmware. Seems like it gets the Nokia VOIP client to re-register every 30 seconds (I've actually done packet traces over WiFi). Still a few glitches occasionally, but the Nokia SIP client with Truphone mostly works through NAT.