How do you enter an unlock code into a Cingular-branded original Firefly phone?

I bought a Cingular-branded Firefly phone on Ebay, and a SIM straight from Firefly. I called AT&T and got the unlock code so that I can use the phone on the Firefly network, but they couldn't tell me how to actually enter the code on the phone, since it doesn't have a keypad.

Firefly can't tell me how to enter the code either.

Does anyone have any ideas?