I'm gonna take a stab in the dark here and bet that thing works just like my BC-700A (made way back in 1992), the BC-350A, and the BC-350C as well. I couldn't locate a manual (PDF style) for my BC-700A but luckily when I bought it used recently - for tapping purposes - it came with the original manual.
All of these "base" style units that are in the same case/form factor all operate the same way, and they all have basically the same type of coverage. I'm not sure if the BC-550A covers 800/900 MHz but I'll bet it most likely does.
Look at the BC-350C manual and see if the functionality is the same, which I'll bet it is:
http://www.uniden.com/pdf/BC350Com.pdf
The amount of user programmable memories might be different, as well as the BC-550A having a "Turbo" feature to speed up the scan rate, but I'd still lay even money on the fact that all of these style scanners from Uniden all operate the same exact way. That BC-350C manual should at least get you up and running to some degree.
Hope this helps... and I'm still trying to locate a proper BC-550A PDF manual also...