Back in May, HTC shared a list of phones that would be getting the Ice Cream Sandwich update within a few months, and the HTC Incredible S was one of them. They held true to their promise of July for the phone as the ICS update is now rolling out to it. More than likely the unlocked GSM version will get it first, then it will depend on your carrier. Here's a quote with some more details,

The update apparently comes in at around 250MB and is being delivered OTA, so thereís no need to rush to your computer and find a microUSB cable. If your phone hasnít already pinged you about an update, it might be worth checking manually. Ice Cream Sandwich will bring some performance improvements, Face Unlock, and HTC has bumped Sense up to 3.6.
Sound off in the forums when you receive the update (or if you have received it already), so we can share in your good news!

Source: SlashGear