Well GOOGLE helps fill the gaps:
PRL = Primary Roaming List (see link at
gsmhosting or another useful link is at
colorada )
PRI = Primary Roaming Interface
SPL = Secondary Program Loader (see links at
wikipedia or
xda-developers )
Hope this helps other newbies
I also found this usefull link, which gives good info on GPSModes and some registry settings:
xda-developers