Each text message is up to 160 characters. Let's assume they're Unicode (they're probably UTF-8 instead, which is smaller) and would require 2 bytes per character and let's further assume these messages aren't compressed (they probably are because text is very compressible), and let's say there's an additional 80 byte overhead per message. That's 400 bytes per message. If you sent one text message every minute of every day, 24 hours per day, for a month, you'd use 17 MB of your 200 MB limit. So yeah, I wouldn't worry too much about it.
