Thinking about getting the 710, got a few questions;
1. Is there an app where I can stream radios? Add my own custom links like .pls or even .asx?
2. Can the battery be extended to a higher capacity? Ebay seems to have a few
There are various radio apps available from the windowsphone marketplace. Have a look at the link below.
Personally I have never had good experiences with batteries from eBay. Additional using a non Nokia battery may void your warranty if the phone is damaged as a result.
Have never tried adding own links but you can always check or ask at the developer sites. I am sure the developer will be able to give you specifics.
I personally enjoy Tune in radio app very much... not sure about those extensions you mentioned.
And I would be cautious about ebay batteries, from what i've read.
But! Mugen has just released a 1500 mAh 710 battery, and i've read very positive reviews of their batteries.