To switch accounts on the smrtPhone Mobile App, you need to go into the Settings tab in the lower menu.
At the very top, under the header "Settings" is the current active account on the Mobile App.
Click on that space, and it will take you to a listing of all smrtPhone accounts to which you have access.
Select the account you would like to use. You will see the rest of the app will update to match the newly selected account including Inboxes, Contacts, and Dialer options.