The only way to install unsigned apps is to have your phone hacked. This means that you would need to flash it with the hacked files.

Another way to install unsigned apps is by signing them (unsigned app) yourself. This is where the trade off of giving your IMEI and getting a .cert and .key file comes in. So technically, you're not really installing an unsigned app in this second method, but installing a self-signed app instead.

Either way works. Good luck!