The option ARM market expanded a bit in 2005, with more originators getting into the business of offering the flexible payment loans to borrowers. Still, the market remained largely dominated by a handful of goliath lending shops. Inside Alternative Mortgages estimates that $310 billion in new option ARMs – or loans that allow borrowers to choose a fully-amortizing, interest-only payment or minimum payment each month – were originated last year. Overall, option ARM products… [One data table included]