I think that a lot of the guys make some very good points here. Phone billing is best for per minute access, this can be for site access or alternatively for specific content. Many people use our
TUBECASH solution in order to mnonetise video content on a per minute basis. Generating 8-10c per minute for content in countries where $20-30 is a huge chunk of cash is a good way of generating extra revenue.
For subscription monthly billing we use an SMS platform that offers a recurring billing option this is after all how most sites generate their revenue as obviously once you have made all that effort to aquire a customer why just throw them away! We charge the end user the additional cost of this service which in most countries is 15-20% and that way you receive the same from SMS sales as you do from traditional methods like card sales, furthermore this means that you wont be canablising your card sales but purely increasing your conversions.
Hope the info helps any one interested in knowing more feel free to hit me up!