He did not authorize the state troopers until near the end of his term as governor, however. I suppose better late than never but he seemed to shift his position after sensing that the country is fed up with illegal immigration.
However, even prior to authorizing state troopers to coordinate with ICE he denied illegals driver's licences in 2003, denied tuition breaks to illegals in 2004 and insisted everyone one learn English. His mind has always been in the right place -- on law and order and national sovereignty -- as opposed to others like McCain, Huckabee, Rudy etc who have always been weak on this issue.
I doubt he would have teamed up with Sheriff Joe, if he didn't have the right idea on immigration. Mitt is endorsed by Sheriff Joe Arpaio of Maricopa County, AZ. Sheriff Joe Tells Why Romney Is the One
I think there were only two states that might have beat Romney to the illegal alien, state connection with ice.