If you like to check your bags curbside at the airport, be sure to pack some extra cash.

One by one, airlines are adding fees for this once-complimentary service.

United Airlines, American Airlines and US Airways, for example, currently charge $2 for each bag dropped off at the curb. On April 15th, Delta Airlines began charging $3 per bag. And that doesn’t include the (expected) tip for the skycaps.

Come May 5^th, when many airlines begin charging an extra $25 fee for checking a second bag, things will get more costly and confusing out at the curb.

In my Well-Mannered Traveler column on MSNBC.com this week, I write about a frustrating experience trying to pin down airline reservation agents on payment options out at the curb. Should I bring cash, credit cards or a personal check? No one seems to know.

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