Is it possible to make a phone call without the use of ons like on this week's Locked Up Abroad?

In the latest episode of Locked Up Abroad "Saddam's Iraq" Tom Lynch makes a call to the Irish Emby from a phone which has had a plate installed covering the phone's ons so calls cannot be made from the phone. However, Tom makes a call to the emby anyway using a sort of morse code with the on used to hang up the phone. Has anyone ever done this before? I just wonder if this is something you can really do.