That sounds potentially useful. Does it work via data connection or USSD?

USSD. You enter the 'to' and 'from' phone numbers and press 'Go'. The 'from' phone rings, you answer, it asks you to wait, then rings to the 'to' phone. When I asked Telna about this feature, they were surprised my SIM had it. They told me it was a feature provided for one of their wholesale customers and not intended for retail users like me. I was actually asked not to mention that I had it. I think it might upset their roaming partners if it became common knowledge. While not a critical feature, it can save a few cents per minute if both 'to' and 'from' numbers are landline rate calls. For example, the cost to call the US from Bahamas would be closer to 20¢/min this way, vs near 90¢/min by their cellular roaming. Please don't call them up and ask about this. They might turn it off.

Two other features I like with Telna are the WiFi calling feature based on a standard SIP client and the ability to call a Telna phone via a SIP address.