I don't mind replying, I know a little about the subject.
We still use this form for those of us, like on a Boeing 767 that do not have GPS. There are a few airlines out there crossing the pond that do not use this advanced tech. As far as the lat/long, yes these are position reports, latitude being the first position heard followed by longitude. The position goes either to Gander, Shanwick, Santa Maria in the Azores, or Iceland radio, all depending on route of flight and position of the tracks across the pond.
Gander and Shanwick share many of the same freqs, which is the reason you hear both. Many times we cannot get one or the other on a given freq, so have to go to alternate freq.
Hope this clears up some questions.