Annuity investors was the variable line, then they made a shift and the great American products became single premium and the flexible products went to annuity investors and they had a whole direct contracting thing going on.
For your question as of 2 years ago you could fund a flexible premium IA as an IRA with 600 per year ie 50 per month.
I just noticed Mass has some 403b flyers on their marketing site, any experience with Mass for 403b's? Only out of curiosity...