Frontier made several changes to their fees (bag fees go up, change fees go down). Also they announced code shares with Midwest Airlines.

Here is the email I got :

There are many exciting changes happening at Frontier Airlines. We’re thrilled to announce a new codeshare agreement with Midwest Airlines that will allow you to travel to more destinations while giving you more options to earn and redeem EarlyReturns® miles.

What the Codeshare Means to You
Now you can purchase a Frontier Airlines ticket (for travel on or after September 8, 2009) to several destinations on flights operated by Midwest Airlines. You'll enjoy new or expanded service to places like Pittsburgh, Cleveland, Washington D.C. and New York – PLUS earn and redeem EarlyReturns® miles on ALL Midwest Airlines flights. Learn more.

Decreasing Fees for Confirmed Alternate Flight at the Airport*
We've lowered the confirmed alternate flight fees (on the same day of travel) from $75 to $50 for Classic tickets and from $150 to $100 for Economy tickets purchased on or after September 8, 2009

Decreasing Change Fees For Economy Tickets
We've lowered the change fee from $150 to $100 for Economy tickets purchased on or after September 8, 2009.

Increasing Checked Bag Fees for Economy Tickets
If you purchase an Economy ticket on or after September 8, 2009 for a flight October 1, 2009 or later, the fee for your first checked bag will be $20 and the fee for your second checked bag will be $30. Ascent and Summit members will continue to receive two free checked bags.