Negative amortization can only arise on ARMs with one or more of the following features:
1) The initial payment does not cover the interest due.
2) The interest rate adjusts more frequently than the monthly payment.

30 Year Fixed Rate Option Loan - A True Fixed Rate Mortgage with 4 different payment options each month. Minimum payment option usually only available for the first 5 or 10 years or until the loan balance exceeds the negative amortization cap.
also known as a 30 Year Fixed Rate Cash Flow Loan

Reverse Mortgage - a loan which allows retired homeowners to receive substantial cash out, in the for of an annuity, lump sum of cash, or combination of the two, without requiring the retired homeowners to make any monthly payments. Not offered by all mortgage companies, and limited to smaller loan amounts and specific property types.

Option ARM - Adjustable Rate Mortgage w/ 4 Payment Options and a rate which adjusts each month. Very popular and common loan in certain states, including California, New York, Florida and other high cost areas due to extremely low (Typically 1%) mortgage minimum payment.

Fixed Rate Option ARM - Adjustable Rate Mortgage w/ 4 Payment Options and a Fixed Rate "start", or introductory period of 3 years or 5 years, up to 7 or 10 years where the rate, payment, or both remain fixed, after which time the rate become variable.
also known as a "Hybrid" Option ARM