Yep, I will also be using passwordbyphone as well...
I understand exactly what you mean when you you say you are concerned as to compatibility issues, and all the scrips 'playing nicely' with each other....
Thats a major concern to me as well
Doing my research, Im lead to believe they all should be compatible... But Im actually heading my bets slightly by doing a few 'different versions' of the same videos, using diff methods... For example, I particularly like the 'tubecash' variant they offer:
http://www.globaladultbilling.com/tubecash/
So I will have my vids using this method on a diff URL but with the same branding... ie main site is 'MyFetishName'POV.com but the same vids using the tubecash method will be on the url of 'MyFetishName'tube.com
So I cant see major problems... But then Im not really offering 'membership' as such... Just short accsess periods when the video can be viewed online... Not the '30 Day recurring' model...