What happens to my SMS number if I downgrade?

SMS is a Pro and Agency add-on. On a plan without it, texting turns off and billing for it stops. Requests set to SMS stop; requests set to Email, or Email and SMS, keep going by email. Your number and its carrier approval are saved for 90 days, so if you're back on Pro or Agency in that time, texting picks up from the same number. After 90 days, the number is released and can't be recovered, and you'd set texting up again with a new number.