Excuse me if I shouldn't ask this kind of question.

Most of us have come across devices that are locked to a certain service provider. For example, a ADSL modem handed out at no cost to its subscribers for Internet connection by ISP. For another example, a Linksys locked PAP2 ATA so that the users can only use it in conjunction with a specific Voip service provider.

I do not know how the lock was first created. I believe some people can unlock them and re-sell them through ebay, although they will not mention it. You are tempted to buy them at cheaper than original price and they give you money back if they do not work.

Assume I bought an originally locked device from people who managed to unlock it. My question is: should I factory reset this device?

I raised this question because my concern are:
- after I factory reset it, will the device become "locked" again?
- after I factory reset it, will any firmware upgrade done after it left the factory be removed? If yes, I wonder if firmware upgrade is still possible as I am not sure if the manufacture will support them (since it may have been 'modified')

If you are against of buying any originally locked device from people who lock it then excuse me for asking.

Thanks for viewing.