the BB doesn't have an antenna port. The only way to mount an external antenna would be to use an antenna adapter or ring attachment. Wilson Electronics makes this kind of kit for Nextel and even has boosters you can use in the car. They don't have a listing on their site for the 7520, but I would be willing to bet they have one available. www.wilsonelectronics.com
This would leave you with the charging which you would need to do with a car adapter or the ac adapter coupled with an inverter.