It seems that the networks are not as generous as they used to be. They must have cottoned onto the fact that customers like Ms VoG generate lots of revenue with the 'txtng'.
3 months unlimited texts are offered by 3 (if you have coverage).
But it stops after the 3 months.
Orange offer 1000 free monthly texts in the evening (after 8pm which is a short evening) if you take out a £15 monthly contract.
Or for £20 p/m Orange offer 3000 texts only
I have no idea if that is sufficient for the really text hungry.
Hope that gives you some ideas.