you don't have to switch e-mails. all you need is to assign a different e-mail address to it.
this is because if you have the same e-mail address assigned to 2 devices how will the person calling you call you on a specific device.
this is how i have my one set up.
iMac - using the e-mail address i use for itunes
iphone - using the cell humber
ipad - using a different e-mail address.
now they have 3 different contact information so they can call me on a specific device they want.