You can manually change the phone number for outbound communications from your Mobile App - allowing you to switch among any of the phone numbers assigned for your use in your smrtPhone account.
Start in the Settings tab of the lower menu.
The second option down says "Caller ID" and displays the phone number that is currently active on your smrtPhone Mobile App.
If you click where it says Caller ID, it will bring you to Your Caller ID List, where all of the numbers available to you will appear. You can select the number you would prefer to use.
Note: If you do not have the appropriate Account Management permissions to edit Caller ID, you may not be able to select/update that section of the Settings.
You may need to contact your Account Owner to find out how to get those permissions.