If i buy a iphone from tmobile will i be able to use it on a other company?

I want to buy a Iphone at t-mobile will i be able to use it on a other company? Yes or no? Or why not.

If you purchase a phone from T-Mobile (or any other carrier) it is locked to that carrier. If the phone is paid for, you can ask to have it unlocked. A T-Mobile phone uses GSM technology so can be used with other companies that use that technology, such as AT&T. The phone would not be compatible with companies that use CDMA technology such as Verizon.

You can purchase an iPhone directly from Apple- the factory unlocked version- and it can be used on T-Mobile and AT&T and other companies as it is not locked to any certain carrier and never was. This is the type of phone I use on T-Mobile and it works great.