You can invite users via Podio or by email.
There are some differences between these two kinds of smrtPhone users.
Users invited via Podio obviously have access to your Podio system whereas those who are invited by email do not.
Those who are invited by email can make calls, receive calls, use smrtDialer, and even use their smrtPhone login for the smrtPhone mobile app - no problem!
The biggest difference is really in how smrtPhone logs calls in Podio.
The key difference is where there is "call owner" - if there is no Podio user, that call will not be logged against a user.