Find nearest Starbucks and check if UMA drops there after 25-30 minutes. If it does not, the problem is in your router or its location in the house relative to blackberry.
If no Starbucks around
just place blackberry near your router and leave it there for 1 hour. Check back and see if UMA is still there. If it is, the problem is weak signal in some places of your house making blackberry drop WiFi and switch to EDGE when you walk there.