I use Bump between my iPhone 4S and my iPad3, both running iOS 5.1.1. It takes some fiddling, but it works for me. What I've found is that you have to hold the iPad in one hand and then "bump" rather hard with the phone in your other hand. Takes practice to get it going, but it's pretty consistent for me now.
All I can suggest is that you keep trying...
Marilyn