I had bought an iPhone 15 at T mobile when I was living in NYC. Being an European, where selling locked phones is illegal, it didn't cross my mind I could be buying a locked phone. However, that is exactly what happened. No one at T mobile explained that the phone was locked and when I returned to my home country, I realized I couldn’t add another phone number because my phone only accepted T mobile SIMS. So I had to unlock the phone. It took much much longer than was first promised and I had to pay much much more than what was first asked to unlock the phone (I paid 300$ for this unlock and instead of taking 7 days it took nearly three weeks to get fully unlocked. At least it works now.