It is possible to load gift cards that have a debit capability to Serve, but Serve seems to be very stingy and many people seem to have trouble with Serve in general but especially as a result of loading gift cards. There is a Serve thread in the MilesBuzz! forum -- just read the last few pages to get an idea of the recent issues.

You would probably have more success paying the credit card bills with Bluebird as other people have reported doing that. I haven't tried it myself. You buy the reload cards at certain pharmacies.