It’s the same issue as web servers dealt with for years. If you are running a small blog and suddenly get flooded with traffic, you have to pay a bunch for server transfer.

To combat this, I do have a few clients using a script that watches numbers and volume. If they start seeing database entries from new numbers and not authentic (taking in other metrics from website visits and other account activity that would trigger a login), it released the number and stops billing for the 10 day period by Twilio and uses another number in the account. Has saved hundreds and thousands of dollars for some customers who have been flooded with SMS messages and spikes outside of normal use.