Need a setting to stop phone speaker

I'm using a backbeat go bluetooth headset on a motorola razr m phone. When I listen to an internet music program (Pandora for example) through the headset and receive a phone call the music goes to the phone speaker. Is there a setting to prevent this in the trial app? Interestingly, when I use music that is on the phone through the Play Music app the music does not play through the speaker. I'm certain I am doing something wrong. Thanks in advance for your assistance.