Based on Citimortgage's policy in their wholesale division, if the borrower wants to get rid of the MI after the LTV was down to 80, they would have to refinance. However, if they choose not refinance, the LTV would have to be reduced to at least 75 in order for the MI to be removed. In this scenario, obviously a new appraisal would be needed. You would need to call the servicing department of your servicer (who you send your monthly mortgage payment to) to get their policy on MI removal.
I hope this information helps. Best of luck!
Total Mortgage Services