I have a Gizmo SIP account configured but it seems that the only way to call a PTSN contact via SIP is to open the phone app, go to the dial pad, change the call type to SIP, and enter the number. Obviously, memorizing a phone number every time is not feasible, so how can one easily place a SIP call to an existing contact's phone number? A work around could be performed by changing the default call type from cellular to SIP but it doesn't seem like that is even possible. Am I missing something, or is this just not yet programmed into the phone app?

That's because you haven't login to the SIP account and change your status to Available/Online.

Once that's done, if you choose a contact, there should now be an option to call that contact as a SIP call.

See how it is on my device - http://pi.pe/onwqhl

Thanks Venom, you led me in the right direction. The key is to check the "Use for telephone numbers" option under "advanced settings" in the SIP account menu.

Does anyone know if there is a way for the call log to correctly identify a caller in the contact list when the call comes in via SIP? Because they come in as xxxxxxxxxx@ipAddress, the log does not recognize the xxxxxxxxxx number as an existing contact and display the caller's name.

In the old days we used to memorise all phone numbers. Seriously.

Some psychologists think that modern phones with their built-in contact lists have resulted in people gradually losing the ability to memorise long numbers in general.