Originally Posted by takeshi
...and with BIS you need to transfer the BIS account to the PIN/IMEI of the other Blackberry. On BES you'd need to do an Enterprise Activation each time you switched. It's not something you really want to do frequently in most cases due to the hassle and loss of historic email with each switch.
or run switch device wizzard on Desktop Manager 4.2 which resolves a lot of the 'lost email/calendar' when switching devices issue.