It's a matter of severity and demonstrable willingness to ignore consequences. Scamming and fraud can earn you a spot in prison for a serious length of time, whereas phone spoofing is probably just a fine or probation, IANAL. In general it defies reason that the people who purposely violate existing major laws are going to be dissuaded by tacking regulations onto their methods.
As I recall, certainty of punishment is generally a far more effective deterrent than severity. In any case, what I think the law would really get is leverage against the US-based phone companies who gateway the traffic onto our phone network.
