Transfer H1: Visa approved and stamped, but not used yet

[rvishen]

Hello All

I have recently(2012) got my H1B Visa stamped for my current Employer (Company A) but am looking to changing my job to another employer (Company B). However I've not travelled on this H1B visa yet. If I change jobs, will my Visa get nullified or can it get easily transferred from Company A to Company B. Essentially, my question is that do I need to use and travel on my H1B visa first to ensure it is portable.

Thanks in advance for considering and answering my question