Hmmm... maybe. We use <cellnumber>@<cell carrier's email-to-sms gateway> for system messages and such, and it works fairly well.
Some of our customers do that for MFA, using the email-to-sms gateway address as the "secondary" email address to receive the MFA code. But, the performance varies wildly. In our local market, it only takes a few seconds for the text to arrive at an AT&T mobile number. In other markets, such as DFW, our clients have reported 30-60 seconds of delay, and they are also on AT&T.
It would be nice if SmarterMail had the email-to-sms gateway server addresses pre-programmed, so users could select their cell provider from a dropdown list, and just enter their 10-digit cell number.
In the year 2023, it shouldn't be this difficult.