<< My bill averages $150/month.
This will save me $1,200.00/year
>>
Once they realize that you are calling that much, they will change the terms of service.
The old MCI friends and family did not bother telling you that the person you were calling had to be part of the MCI network for the discount.
Double check the actual terms of service, knowing MCI, I suspect that will be the case.
The target of your call may have to either also be on this plan or an MCI customer for you to not get hit with extra $.