Interesting. Unless you are having no problems pinging in other EDGE areas (at least 7-10 miles) away from your home, your local tower is not likely the problem. Have you been able to test other devices at this location, or test the hotspot in a different location? If we have not already, support will need to pull up your location to confirm the coverage and that there are no known tower issues.
A week or so ago, I tried the mobile hotspot in St. Croix Falls, WI, about 15 miles south of our cabin. This is also an Edge area. The hotspot had 4 bars. Pinging the DNS server worked MUCH better, even though the ping times were still all over the map (from 250 ms to 3000 ms).
This weekend, I was at the cabin trying to use the hotspot again at 1AM, when you would think that there would no no network congestion. Again, sporatically the pings would work fine for about 1-2 minutes with 250ms to 3000ms ping times. Then I could go for an hour with continuous timeouts. During the timeouts, I could occaisionally get e-mails to send and receive, even though it was PAINFULLY slow. This was with my hotspot outside with Edge coverage showing solid 2 bars.
Years ago, at the same cabin location, I used to dial up to my ISP using my old T-Mobile Nokia phone using Circuit Switched Data (the connect time came out of my minutes). The connection was only 9,600 baud, but it worked MUCH better than EDGE using my mobile hotspot.
I don't have any other T-Mobile devices to test at my cabin, so I can't tell if the problem is the MF61 mobile hotspot or the T-Mobile network. I would be very interested in getting more feedback on this, as I would potentially be interested in using an unlocked iPhone on T-Mobile, but only if it works reliably at my cabin (I'm willing to live with slow connections, but they have to be reliable).