If you're using a generic device you don't have too long to wait... HTC will be starting the rollout in October for generic devices with rollout to all devices (including operator branded units) set for completion before Christmas (subject to operator / Google approvals etc. of course).
The forthcoming One X+ will ship with Jelly Bean 'out of the box' as will the One XL destined for EE.
Unfortunately we don't have schedules for the One S yet, but we'll keep you posted if we hear anything!
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