If you're using a Sprint Nexus S 4G phone and want Ice Cream Sandwich, you're in luck. A build of ICS has leaked and it is believed that it is the same version that the carrier will soon release. The build number is IMM26 and so far the reports are it's stable.

If you'd like to install the new build you can head over to XDA via the link below, but be aware that you install it at your own risk.

Alternatively, you could just wait for Sprint to release the OTA update which should be out soon.