Random ? about the mechanics of GM's contacting each other

In the past, land lines and fax machines were how GMs would reach each other on and around draft day. Obviously those days are long gone. We have heard JS refer to "calls and texts" with other GMs to gauge trade interest, set the terms of a trade, etc. Goes without saying that since there's limited time to make picks on draft day, time is of the essence, as is the ability to be assured you can reach someone when you need to.

Does anyone know for certain if this method of contacting one another is done as simply as personal/work cell phone to personal/work cell phone? Seems like there's a ton of room for errors/issues there, with respect to bad signals, network outtages, wrong numbers, dropped calls, busy signals, etc.

Or do you think there's some sort of a group network of the 32 GMs sort of like Signal or Whatsapp, whereby the users are easily identified and reached, there's the ability to private message, send a group message (eg anybody interested in a late round swap?), have a private video chat, etc. Just wondering if there's a more secure/sure way of doing this...one we may or may not be aware of.

Thanks for any intel.