I'm still using them too. Coverage has been excellent. Overall I am satisfied and I really like not having a contract.
But they have a serious problem with communicating with customers. Things change and you don't find out until it happens.
The things happening are out of their control - they are just a reseller, Verizon and Sprint control what is available and what is allowed (i.e. bandwidth caps). Verizon got upset at some of the "kids" running bit torrents and heavy video usage, racking up 50-100GB+/month and put their foot down. Initially Millenicom tried to mitigate the damage and tell people to keep it under 10GB/month. But apparently that didn't work or Verizon didn't go for that either once their attention was aroused. So it got capped at 5GB/month.
Millenicom apparently worked a deal with Sprint to offer a new "unlimited" plan for an extra $10/month and is not offering any new accounts at the $59.99 rate on Sprint. So they now offer 5GB on Verizon (where Verizon has coverage) for $59.99 or Sprint with unlimited (within reason I am sure) where Sprint has coverage, for $69.99. The are also part of the rollout of WiMax. They are offering a pretty good plan with that in the limited markets where it is available. But unless I am mistaken, it isn't intended for mobile access at this time. The person signs up for coverage in a single market. But in that area they get something like 7Mbps download speed with no bandwidth limits.
I am on Millenicom's Sprint based unlimited plan. My connection speed varies between 400Kbps - 1.3Mbps depending on the tower and how/how many people are using it. For example the tower I am on right now must have either one of those heavy users on it or several regular users in the evening/night. Resulting in a speed report like this even with a strong signal:
Note, somebody is uploading heavily on the tower right now to get the upload speed down so bad. Also, the reference to the city is just where the number it "dialed' into is at. I am in Chattanooga, TN but the number it dialed into was in Jacksonville, FL. I have used some the methods posted on the Internet to try different dial in locations and found no significant difference. The bottleneck is usually the local tower.
Another benefit of Millenicom (besides no contract) is the taxes (or lack of). Whereas the other carriers add all kinds of taxes to their plans, the rates at Millenicom include the taxes. So on a $59.99 plan, that is exactly what you pay.
And even now, when you call customer support, you get somebody that is U.S. based and speaks English as their first language. I'm not prejudiced about languages, but I speak one language for practical purposes and bits of a couple others. If I need support, I want somebody that can understand me clearly and that I can understand them clearly.
Further in praise of their support personnel, when you call them and it turns out to be a problem with the backbone provider (i.e. Verizon) they don't just give you another number to call and say bye. They conference call the other support with you and they stay on the line.
So in conclusion, I am happy with it.