Is there a USDD gate in nature with the opening of a session on demand

Question

Telecom operators

I'm actually looking for such a thing

. Now communication with subscribers occurs via SMS, the subscriber sends a request to some number (single number), we send a response.

SMS go for a long time and disappear in the open spaces of operators, and most importantly, the subscriber needs to pay for them, I'm trying to win using USSD

In this regard, several questions arose
1 Is it possible to send a USSD request from one operator to another
2 Is there any number to which you can receive messages from any operator in the world

Well, actually if there is none, maybe someone knows a service that allows you to receive SMS, but so that it costs nothing to the subscriber who sent it?