1. UMA is tied/was tied to the T-Mobile Hotspot initiative. Since they are pretty much out of that business other than in some airports and hotels, it's not a priority.
2. Without UMA when you go out of the country, you have to pay through the nose on roaming and roaming makes T-Mobile money. Thankfully client Truphone works on WiFi on the Android devices. That mostly solves the problem which Om solves on his Blackberry with UMA.
3. With the Wal-Mart move, T-Mobile is following a very successful strategy of Bouygues which powers many of the HyperMarket retailers' mobile phone offerings in France. This indicates that they will likely have deals with Costco, Sam's Club, Target and eventually even supermarkets.
Most of this tells me also that T-Mobile's parent, DT, in Germany wants to see revenue increase so they can sell the USA operation to either Vodafone, Orange or Telefonica, the three most likely suspects. Vodafone wants to get out of their deal with Verizon in Verizon Wireless and the opportunity to be the USA's other GSM carrier is too much to pass up on.