the only agency we found in the internet that really talk about the service they offer. the webpage is only chinese, but if you crawl down on the start page, you will find the english service description ;-) they offer a special massage for rmb 1000,- for one hour, so more expensive but clear service.
link: Shanghai Girls Massage
warning: till now, Shanghai Nightlife Guide did not check the service,
and also no customer till now recommand it, so be carefull. If you have experience with the agency, please leave a comment.