[Gta04-owner] Detect Call Hangup / Option Datasheet

[Dr. H. Nikolaus Schaller]

> That is why every serious voice modem manufacturer adds a vendor command
> for call state notifications. And more important why they make ATD123; a
> non blocking call where OK is returned right away. However it seems that
> nobody told this to Option. Polling via CLCC is still nasty, but doable,
> but having a blocking ATD123; is just pure stupid.

I think it does not block if AT+COLP=0