The easiest way is to have a SIP gateway that uses a too long number to display. Usually it's around 12-13 digits for the subscriber number depending on the cou

The easiest way is to have a SIP gateway that uses a too long number to display. Usually it's around 12-13 digits for the subscriber number depending on the country code, so all digits before that (after in SIP) will be cut out on most phones. I think the relevant spec for that is E.164 which enforces 15 digits overall (1-3 for country code and 12 for subscriber number). There are also lots of SIP gateways that have an ISP license or a phone provider license. They're the same types that allow to fake the numbers for their customers, and usually you can transfer some still in use mobile numbers to them as well. Because apparently law enforcement doesnt do anything against them. And yes, never use 2FA via SMS. Never.