From a security point of view, if you're using anything before LTE?, the carrier verifies the SIM, but the SIM doesn't verify the network, which means your devices could get tricked into sending through a rogue network that could see your 2fa codes and destinations. Similarly, I don't remember when mobile network cryptography got good, but older networks are definitely eavesdroppable. You don't want your 2FA codes eavesdroppable beyond the minimum footprint for obvious security reasons; carriers visibility is unavoidable with SMS 2FA, but maybe there's a gain with a device you control vs an aggregator (and aggregators commonly use other aggregators for some of their routes), although you really can't know how a carrier delivers messages destined for other carriers.
If you're going to do this, you need to do it as part of a system where you use many providers and monitor success.
If the rate is high, it's almost certainly going to get blocked. But then, it may work better for some destinations than any commercial provider. Or it might continue to work when the commercial providers have outages, or the carriers do maintenance on their external connectors.
Some of the SMS aggregators use regular SIMs to send some messages, or contract with others to do so, it's generally called a grey route. Usually with more specialized equipment and more SIMs, but same basic idea.
If you're going to do this, you need to do it as part of a system where you use many providers and monitor success.
If the rate is high, it's almost certainly going to get blocked. But then, it may work better for some destinations than any commercial provider. Or it might continue to work when the commercial providers have outages, or the carriers do maintenance on their external connectors.
Some of the SMS aggregators use regular SIMs to send some messages, or contract with others to do so, it's generally called a grey route. Usually with more specialized equipment and more SIMs, but same basic idea.