What release of Sol10 do you have ?

cat /etc/release to find out.

This applies to S10 HW2 and S10 U1 only. The only way to get the USB driver
support installed in a new install is to load the SUNWCXall cluster. This is the
(Entire Distribution + OEM) cluster. Failure to do so will cause the USB to be
nonoperational.If you loaded a different cluster you may manually add the
following packages to get USB support:
SUNWuedg
SUNWugen
SUNWugenu
SUNWuprl
SUNWuksp
SUNWukspfw
SUNWusb
SUNWusbs
SUNWusbu
SUNWlibusbugen