Check /var/adm - see if your messages file(s) can be removed (well, emptied - you probably don't need to remove them) if not needed - look throughout that directory to see if you can get some space back.

As far as growfs, if you read the man page for it, it looks to be used for metadevices which you aren't using (DiskSuite). I don't know if it would work on your file partitons.

How much more space do you have? If it's larger than /var, you could mount it as /mnt and dump /var into it then remount /mnt as /var.
Or, if /var/adm is huge, you could use the space in one of your free partitions (slice 3 assuming it isn't swap) and then have /var and /var/adm as mount points.

You might want to post the partition table of that disk ( c0t0d0 ) from format - then we can tell where the free space is and which options would be easiest to gain more space.