You should not attempt to power the bell circuitry from the Arduino. Doing so could overload the regulator or damage the Arduino. Instead, control the bell (that is, the 5 to 12 V boost circuit in your diagram) just like you would a motor, with a transistor switch or a motor driver and using a separate power supply. If that power supply is 12V, that eliminates the booster.
It has to be somehow connected to the shield/arduino otherwise it can’t be activated when a call is received. Which I haven’t figured out how I’ll do yet but I know it’ll be through the gsm. Also I would prefer that a single battery/ps be used. The current it draws is said to be up to a peak of 75mA or 10mA depending upon when you ask.
What does that Inhibit wire do?
I dunno it just was there. I assume if powered it would silence the ringing. I think maybe it would be better to find some solution that used as little power as possible though. Possibly by turning power on and off to the ringer circuit?