Having been through this before (posted below), it occurs to me that Sun/SI may not have any idea whats going on here. This could all be the result of an overzealous paralegal just trying to make-work. There are likely geeks at Sun/SI who use and enjoy Sparkfun products. One well placed call to the right guy at Sun/SI could solve the whole thing. They could reach a $0 "settlement" where Sun/SI protects their mark by "taking action", and Sparkfun gets to go on and conduct business as usual.

On the other hand, as I said, if Sun/SI really wants that name, there is likely little Sparkfun can do to stop them taking it.

Edit: Fujitsu is also connected to SI as a founding member.