If I already have a Jott account, do I need to register my iPhone number to use Jott for iPhone?
No, you can login to the application with your current phone number (user name) and password. If you would like to be able to call Jott’s number to send a Jott from your iPhone, that number must be on your Jott account. You can add additional phone numbers via the Phones section of Settings while logged into your account at Jott.com.