MortgageIT, a fast-growing independent mortgage banker based in New York City, plans to go public and begin building up a retained investment portfolio of ARMs and adjustable-rate MBSs. The company funded $11.9 billion of mortgages through several different production channels in 2003, with most of its volume in wholesale. That was up sharply from $7.4 billion in 2002 and $2.9 billion in 2001. MortgageIT plans to continue focusing on the prime, conforming market, the