Unlocking second sim possible?

Here is the issue with the sim unlock policy:

• T-Mobile subsidizes the hardware to keep you in a contact which prevents you from paying the phone off early. It would cost the consumer $400-600 depending on the promotion.
• I don't see a situation where I would pay the phone off ever. I would just keep replacing the phone every 1-2 years. Which is what T-Mobile wants to stay under contact but continues to prevent the user from using the 2nd sim.
• If you are looking for a second line from T-mobile, the cheapest line you can get to put on the phone is $30. You have no need for data but it's part of the package anyway. They should consider doing an "add a line" like they do for watches and tablets for $10. 
• You can get a second line UNL Talk and Text with no data for $9 from other carriers that use T-Mobile. 

There are some posts on being able to pay off your phone and continue to get the promo paid out. I spoke to T-Mobile today and they said that if you pay it off there is nothing left for the promo to pay off so it just ends. 

For those that mention the DIGITS line, if you have no data in your area it never works. Great if you are on wifi all the time but it's not reliable as having an actual line. And Google Voice is the best option however you just end up forwarding the number or calling through a bridge. You can't really separate your personal line from your second line. 

Unless T-Mobile can do an add a line for $10 to the second sim, I don’t really see how any carrier will let you use the T-Mobile unless you bought an unlocked phone directly from Apple.