I have the 520 and use it as a music player only. I have a 920 I use as a phone. My 520 has a 64GB card in it. With 64GB, the phone can be a little slow at times. I have deleted everything I can and use it in airplane mode. The battery lasted over a week in standby mode. However, once I downloaded Nokia Music I only get about a day and half.
I use this in a Mercedes and it will display the name of the song from Bluetooth on the dashboard it will also automatically resume from the what I was listening to before I stopped the car.. I also have a Ford with Sync, but do not use it in the Ford, it does not treat Bluetooth as nice, so I have a 64GB thumb drive for that. There are other issues with it, but most of the people have already shared them. It makes a nice inexpensive music player. I received my 520 free and only had to by the 64GB card, which was on sale.