I want my mortgage backed mortgage backed mortgage backed bonds, I want my mortgage backed mortgage backed mortgage backed bonds; iShares mortgage backed bonds, MBB style!OK, apologies to everyone for that.iShares has just listed an ETF that tracks mortgage backed securities with ticker MBB.I just found out this ETF a few minutes ago so I don't know much about it. It obviously has merit at different points in the interest cycle and pre-payment would not seem to be an issue like with individual GNMA pools (but we'll see if that is right or not).I also wonder if there will be utility in tracking the spread between this ETF and one of the treasury products.