Questions on Unlocking my AT&T HTC 8x

[channing0214]

I just recently switched to T-Mobile from AT&T and will be selling both of my AT&T Windows Phones.
The HTC 8X was not under a contract so it is the first one that I will be selling.

I received the email today from AT&T with the unlock code for the phone and instructions on how to complete the process. The steps are listed below.
1. Power off the device.
2. Remove the SIM card from the device.
3. Insert non-AT&T SIM card.
4. Power on the device > enter the eight-digit unlock code > press Enter.
5. Insert the AT&T SIM card and power on the device.
6. The phone will now accept a SIM card from any service provider that uses a SIM card.

The step I had a question about was number 3. I currently have a T-Mobile sim card that is active will all of my information on it. I can use this card to complete the process even though I will not be using the HTC 8x with T-Mobile and just selling it.....correct? I guess it just seemed odd to me that I would be putting in an active sim card.

Also, it says to Re-Enter the AT&T Sim Card and Power on the device. Once this process is complete and the phone is powered back on can I now remove the AT&T Card and discard it, or does it have to stay in the phone?

I have just never done this before and I just wanted some re-assurance that this process works smoothly and I will be able to sell the phone unlocked with no issues whatsoever.

Thanks for the Help.

 

[radmanvr]

It does not have to stay in the phone. and yes a tmobile card counts as a non att card

 

[channing0214]

It does not have to stay in the phone. and yes a tmobile card counts as a non att card

Thank you, I just want to make sure I do it right the first time since they stress that you only have a certain amount of tries or else you won't be able to unlock it again.