I've had a look at these on ebay and to me everything looks ok, it's not illegal to unlock your phone if its on pay as you go or contract at any time. If you're on a contract you still have to make payments to whatever company for the minimum term of the contract so they still get there money. Pay as you go phones you have to pay for so they get there money (even though they will probably try to tell you that they get the phones cheaper from the manufacturer by locking them to their network)
The Subsidy codes being sold on ebay are only for motorola phones so I'd say that subsidy is just another name for unlock code. (
http://en.wikipedia.org/wiki/Subsidy_Password) There is nothing illegal about making software that can generate the codes.
Almost any phone can have an unlock code generated from the IMEI, I know this because if you contact your current network and provided you meet required criteria they will give you a code and instructions on how to enter it.
I recently tried to get an unlock code for a samsung phone from o2 but they wouldnt issue one as the phone hadn't been used on the network for 12 months yet.
Or you can just go to any independant mobile phone repair shop and pay about £10 for them to unlock and test it for you.