I believe smbmount is only supported on linux, as for smbmount to work your kernel has to support the smbfs filesystem. I could be wrong about this, but I don't believe there is smbfs support for the solaris kernel yet.
If you just need to copy files from CIFS Servers, smbclient and smbtar can do that for you, but you can't actually mount the CIFS share as a file system on Solaris yet.
This from Sun's web site:
Samba provides SMBFS file system support in the Linux kernel, which enables folders shared from Microsoft Windows systems to be directly mounted on the Linux file system, using the smbmount command. However, the Samba development team has not yet ported the SMBFS kernel module to the Solaris platform. For this reason, Solaris can not use the smbmount command to mount folders shared from Windows computers. In the Solaris platform, the smbtar utility accomplishes this instead.