[OnePlus 7T Pro (Regular & McLaren) Guides, News...] TEKHD:
Good News (This is a Link)

Ordering Dual SIM tray right now... We will probably use it in the future. (assuming 7T Pro McLaren is in the same boat as 6T)

A T-Mobile phone with dual sim is simply amazing/priceless. Specially one with so many bands and carrier support like the McLaren 5G. We have to be careful, we can't flash the modem partition / take extra caution with the modem part. (That tiny detail is very important) We can easily end up with a brick if we mess with the X55 5G Modem.

Open the OnePlus Community app and search for "OnePlus 6T T-Mobile variant has dual SIM hardware!!!" (without quotes) I am sure there has to be extra info here on XDA too.

Order placed...

See Attachments -> Yes... Today I decided to search... Lol... I am all about Samsung. (and HTC long ago) Let me retrain my mind with this OnePlus universe...

I literally got the OnePlus just because of these 4 main reasons:

1. Qualcomm 855+ (I am a CPU enthusiast)

2. 90Hz Display

3. No freaking camera hole on screen (Hate the damn hole on my Note 10+ & I actually get more screen real state on the OnePlus compared to the Note 10+ -> even with a smaller 6.67" vs 6.8" screen / Damn Hole prevent apps from running full screen...)

4. X55 5G Modem

...now this is getting even better with the Dual Sim.

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Antutu Benchmark included if anyone cares... Great Results - Defeated 99% of users - (see attachments)

Edit: I am sure we can modify the T-Mobile ROM (with root obviously) and make it dual SIM compatible without the need of flashing international ROM. It would be great to have latest international OnePlus 7t Pro firmware & latest T-Mobile McLaren 5G firmware so I can compare. We just have to add/edit a few lines. That's all. The idea is to keep Wi-Fi Calling/VoLTE/HD Calling/RCS/Video Calling/Etc plus Dual SIM.

As soon as I can get my hands on latest firmwares (both OnePlus 7t Pro & T-Mobile McLaren 5G I can start making things happen. (Not only about Dual SIM, also many other features that I guess are available on International Firmware and not on T-Mobile? If any? I am honestly not sure what's the real difference between the 2 here in OnePlus universe... But from where I come from (Samsung) there are many features not present in US variants. Just to give a quick example, Carrier Samsung variants don't have Bluetooth Tethering, No Spam/Caller ID protection, even the Data Toggle is missing in US carriers, etc etc etc... I see Bluetooth Tethering, I see Caller Identification and even a Data Toggle on my McLaren... So... maybe T-Mobile is keeping all features?

I have Exynos (International) Samsung Note 10+ and Snapdragon (US carrier) Samsung Note 10+, so I can easily compare things, but I have no point of reference on how different (if any) is International OnePlus vs US Carrier OnePlus. (beside the Dual SIM that we all know) If anyone with OnePlus experience/Developer can enlighten me on what are we missing?

In other words my question is... if Joe comes here and says, Hey I want to flash International ROM on my T-Mobile OnePlus variant... What's the point? Maybe Joe doesn't like the T-Mobile Boot Splash Screen? Lol (that you can easily remove/swap with root) Joe just wants faster updates? I mean... What are the benefits? What are we really missing?

This might sound stupid, but this is how I work... If anyone can go thru the menu options with one International OnePlus 7t Pro on the left and one T-Mobile McLaren 5G on the right and see all features and options 1 by 1... and look for missing options on our device. That's how ROM Development starts...

Edit 2: Let me repeat again, (by reading other posts around here) DO NOT Flash International McLaren firmware on your 5G McLaren... Your Modem is completely different.