I'm on a plan paid by my employer. To me the benefits are:
1. Increased access ability. I end up on the back side of a hotel sometimes with little TMo signal. I almost always have a hotel wifi connection. That along with my Travel Router and I almost always have UMA at the hotel.
2. Overseas travel. This gives you free calls (pulling from your minute bucket--maybe.) Even without the H@H plan many have reported that these minutes don't even get deducted from your minute plan either. This can save the company hundreds of dollars on overseas to home calling.
3. Faster browsing. Even without UMA if you can just get a wifi connection your browsing speeds are much better with wifi connected.
Side benefit: I posted this in another thread a minute ago but I'm currently at DFW (Tmobile Hotspot) and am tethered to my UMA connected BB and posting on this forum for free.