On an FHA loan, to avoid having to pay the annual/monthly MIP (it's called "MIP", for "Mortgage Insurance Premium", on FHA loans because they are self-insured,and "PMI" means "Private Mortgage Insurance") you'll need to put at least 22% down and take a 15-year term or less. However starting on June 3rd 2013 even with those parameters FHA will start charging annual MIP in the amount of .45% of the loan amount per year (i.e. on a $330k loan amount it'd equate to $123.75/mo).
However did you know that you can use conventional financing and your mom can so-sign and be able to use her income to qualify? There are two primary forms of conventional financing - Fannie Mae & Freddie Mac. Fannie Mae programs WON'T allow an occupant borrower & non-occupant co-borrower to combine their income to qualify however Freddie Mac loan programs will. Since you & your mom both have excellent credit, then I strongly recommend you look into using a Freddie Mac loan program to purchase rather than FHA financing as it'll save you more money.
Shane Milne | Lending in all 50 states | NMLS #81195
shane@thebesthomeloans | 949-273-4161 direct