How is avoiding PMI different on Summerville versus Sullivan's Island?

Avoiding PMI works the same way regardless of town, since it comes down to the down payment size relative to the loan amount rather than any location-specific rule. What differs between Summerville and Sullivan's Island is the price point itself, since a Sullivan's Island home typically requires a much larger down payment in dollar terms to hit the same equity threshold as a comparable Summerville purchase. Brian Beatty can run the numbers for a specific property in either town before you decide how much to put down.