about locked iphone

Your plan is a prepaid plan so that's what you need to do to meet the requirements. You can go to a Tmobile store to confirm this if the rep is knowledgeable.

so is it valid if i add it in the form of prepaid plan charges 

After you put your Tmobile Sim card in the phone the add $100 and wait the required days.

This means I need to pay a lump sum of 100? pay to where?

I'm pretty sure it's $100 after the new imei is detected not for funds already  made.

KarlChennnnn wrote:

Thanks! Let me summarize, I just need to insert my existing SIM card into this locked phone and unlock it after recharging more than 100$ this year, right?

The device still needs to be used on the network.  Even with $100+ in recharges, the device needs usage on the T-Mobile USA network.  Not roaming usage and a minimum of 14 days use on the T-Mobile network might be required.

Also, iPhone SIM unlock requests are sent to Apple to process.  These SIM unlocks can take upwards of 3 weeks and sometimes longer.  This is solely on Apple's end.  All T-Mobile does is verify your SIM unlock eligibility and then sends the SIM Unlock request to Apple.  

Thanks! Let me summarize, I just need to insert my existing SIM card into this locked phone and unlock it after recharging more than 100$ this year, right?

KarlChennnnn wrote:

do i need to recharge 100$ at once or does it only require that the amount previously recharged exceeds 100$?

More than $100 in recharges within a calendar year.  If you recharge a total of more than $100 over the next few months.  That will meet that requirement.

do i need to recharge 100$ at once or does it only require that the amount previously recharged exceeds 100$?

You can check the prepaid conditions in the SIM Unlock Policy for the requirements you would have to meet.  

https://www.t-mobile.com/responsibility/consumer-info/policies/sim-unlock-policy