This is an opportunity with a pretty limited audience — Wisconsin residents only with mileage balances in Frontier Early Returns — but for those members this is huge.

Via NotiFlyer, Frontier will allow you to bail on the Early Returns program and move all of your miles to Delta Skymiles.

Frontier elite members taking advantage of the offer will be enrolled in a Delta status challenge, receiving 90 days of silver status with a requirement to fly 8,000 qualifying miles or 10 qualifying segments on Delta within 90 days to retain that status.

It’s all or nothing with the conversion of miles, but Frontier members with elite status will still keep their existing status.

The offer is valid through August 31, 2012. It’s a one-time offer, so if you have Frontier flights coming up you may want to wait until those credit to the Early Returns program before initiating the transfer. While points may take up to 8 weeks to post over at Delta, the mileage balance that will transfer will be the Early Returns total as of the date of the transfer request.

Frontier’s offer FAQ is here.

This is the only time I’ve ever seen anything like this, with an airline that continues to operate. Frontier says it’s because they’ve ratcheted down their Milwaukee flying so much since acquiring Midwest Airlines. I have to imagine that Delta is basically buying customers from Frontier in an unorthodox transaction, normally this would be an expensive option for a carrier to undertake in redeeming its miles for the miles of another carrier.

And as for whether or not to do this, it seems like the biggest no brainer in the history of earth like those XM Radio commercials for Lennox Financial are wont to say…