Guaranteed hours with AmericanMobile

My wife has been with intelistaf the last 3 assignments. Overall she has been pleased with them, however she is considering changing to americanmobile because they have an assignment where she wants to go and intelistaf does not. Intelistaf has always had guaranteed 36 hours of pay per week written into the contract. American mobile is saying that they can not do this. When my wife started asking about this the recruiter tried to blow it off and started mentioning all of the "wonderful" benefits they had to offer. What do you guys think? Have you had any bad experiences with americanmobile?