These are special "StarStar" numbers offered by StarStar Mobile: https://www.starstarmobile.com/
So the asterisks don’t really represent anything, they’re literal representations of *
key/button you find on any phone.
While I’m not familiar with the details of the implementation, it appears to be a clever hack on VSCs, which are how telcos let you control various telephony features via the network itself:
https://en.wikipedia.org/wiki/Vertical_service_code
So presumably the Star Star folks have struck a deal with the big telcos to route any calls starting with **
their way, and they can then forward the calls to the paying customers.
Credit:stackoverflow.com‘