I was having some problems with an ant USB stick and my Galaxy S2, as I metioned in this thread: http://www.thisisant.com/component/option,com_fireboard/Itemid,146/func,view/catid,30/id,3413/
The problem seems to be that Samsung blocks the USB Host API in some phones, as the Galaxy S2 and the Galaxy Note for example.
Solution: install a custom kernel, in concrete the Siyah kernel has the USB host API enabled, you can download it here: http://www.gokhanmoral.com
I have tried it with cyanogenmod 9 RC2 but should work with stock ROMs and others.
The problem is that installing a custom kernel or ROM voids the warranty and isn't recommended if you don't know well what are you doing, as there is a probability of breaking your phone.
Just after flashing the kernel, when I connected my OTG adapter with the ANT stick2 plugged in, a dialog appeared asking for launching the ANT USB service.
Then in the ANT+ demo I could pair my HRM, also ipSensorman shows the sensor correctly.
What I can't get to work by the moment is Endomondo, it doesn't detect the ANT device and just jumps to Bluetooth search...
I'll keep investigating to solve this issue, as my intention was to use the ANT HRM so it is integrated with my bicycle runs.
Hope this helps someone when getting ANT working.