i had been having issues switching the pairing for my beats wireless between my macbook and iphone. but i think i finally cracked it.
first, get the headphones paired with each device. on macbook, this is done in the bluetooth dropdown menu. select "set up bluetooth device" and choose the headphones while the headphones are in pairing mode (pairing mode = flashing red and blue light, achieved by holding the power button for extra seconds). on the iphone, this is done in settings > bluetooth > and select the beats wireless, while headphones are in pairing mode. if you're having trouble getting the headphones to pair with either the computer or the iphone, make sure both the phone and computer have bluetooth turned on and are discoverable. also make sure you start with the headphones off, and then hold down the power button for extra seconds (not just until the light turns blue, but until it makes an additional noise and flashes between red and blue. for me, i think the problem was that i was turning them on, and THEN turning them into pairing mode. it works best if you go straight from "off" into "pairing mode" without releasing the button in between.
now, to switch between devices:
First, turn off the headphones. then turn headphones on, but go straight to pairing mode. (so, do NOT press for a few seconds to turn it on, then press for several seconds to go into pairing mode. instead, DO press "power" for several seconds to go straight from "off" to "pairing mode.")
Now, to connect to macbook: while headphones are in pairing mode, select them from the bluetooth dropdown menu. select "use as audio device." should work perfectly.
Now, if you want to switch to your iphone: power off the headphones. then turn the headphones on, but go straight into pairing mode (hold for several seconds until the light flashes blue/red, NOT for a few seconds until it goes blue). while in pairing mode, go on the phone into settings > bluetooth > and select the Beats Wireless. that should do it. if it still doesn't work, then make sure "beats wireless" is selected from the airtunes menu in the music app (the little box with the arrow in the bottom right corner). but that should be selected automatically after pairing.
hope this helps! i found the trick was going straight into pairing mode from a powered-off position. if i just turned on the headphones, they would immediately try pairing with the device they had last been used with. then the headphones would get confused and just shut down. but when i follow the steps outlines above, it switches back and forth easily every time. i wish there was a way to do it without going into the iphone's settings every time (like you can with airtunes) but such is life.
note: if your computer doesn't have a bluetooth drop down menu in the upper right set of menus, then you can add it through System Preferences > Bluetooth > Show Bluetooth Status in the Menu Bar