Of course, we did thousands. Nowadays it's not legal to lock phones in the UK so no need for them now; in other countries I guess it's too difficult to unlock.
If you were me, and you had a Samsung GT-E3210 dumb phone (keypad phone) made about 2013, that would only accept your current SIM card (the 2nd SIM card you've used with this phone) how would you go about unlocking it please ?