T-mobile is the GSM service provider in USA. This mobile service is owned by German company. T-mobile entered into USA by acquiring four US mobile service providers. You can find many unlocked phones for tmobile in USA at different stores. This mobile company generally provides pones which can only be used with t-mobile sim card. You can use sim card of any other service provider unless these are unlocked. These service providers in USA generally sell cell phones which are programmed for using with sim cards provided with mobile phones. You cannot switch service provider just by changing sim card. Headquarter of T-mobile is located in Washington in United States. In USA you will not find unlocked phones. In big mobile stores established by service providers will only sell you cell phones which are locked. This means that you can use phone with their sim only. After you take out sim from phone then your handset will be of no use because you cannot use new sim with this handset.

If you are living in USA then you can find small retailers which will provide you with unlocked phones for tmobile. You can buy sim card separately can use it on your unlocked phones. If you want to use tmobile sim card into unlocked cell phone then you have to insert t-mobile sim card into unlocked cell phone. After this you have to contact the customer care executive to re-program your cell phone to work with t-mobile sim card. You have to visit service center established at different locations in USA. These service centers will reprogram your mobile phone to work with t-mobile phones.

Unlocked phones provide facility to change service providers anytime you like. But with locked phones you are not able to change service provider frequently. You can also pick mobile of your choice and later on reprogram it to use service provider you like. Unlocked phones for tmobile can also be purchased from other countries. These cell phones will also work with t-mobile sim cards. Since t-mobile is reputed mobile service Provider Company so it is better that you choose this company for using mobile services. You will get roaming facilities in many countries without paying extra charge in countries where t –mobile company is working.