During the monthly plan, you receive incoming texts as email through NumberBarn. Two-way texting depends on the carrier the number is on.
After buyout, when you port the number to your own carrier (Twilio, OpenPhone, etc.), full two-way texting works the way it does on any business number on that platform. Text capability is a function of the carrier, not the number itself.
If you specifically need a vanity number that can text out today, the simplest path is to buy out and immediately port to a VoIP provider that supports texting (OpenPhone is popular for this). Tell us this is your plan and we can set expectations accordingly.