Well, that's unexpected. It turns out an unlocked Verizon Samsung Galaxy S10 5G can connect to T-Mobile's as-yet-unlaunched millimeter-wave 5G network.
Prominent speed tester and Ookla Technical Evangelist Milan Milanovic ran a test on T-Mobile's network using Verizon's phone and scored 493Mbps—not quite the gigabit speeds we've seen with Verizon and AT&T so far, but really good considering the limited airwaves T-Mobile has to work with.
T-Mobile's feat becomes greater when you understand that the carrier is using much less spectrum than Verizon is. Allnet Insights says T-Mobile is using 80MHz of spectrum in New York, which would make its theoretical maximum speed 500Mbps, but I've also heard that T-Mobile is using 100MHz, which would make the theoretical maximum 625Mbps. Verizon used 400MHz of spectrum in Chicago to achieve the 1.17Gbps speeds we saw in recent testing; with 400MHz, theory says you could get up to 2.4Gbps.
At first glance, T-Mobile appears to be using its spectrum more efficiently than Verizon. But Verizon's network was also a live network with other people using it. T-Mobile's network probably only had Milanovic online at that moment.
Although it hasn't been officially launched, @TMobile #5G seems to be blanketing Manhattan and performs wonderfully! Unlocked VZ @Samsung #S105G @EricssonNetwork ?????? pic.twitter.com/YAPywpxGTp — Milan Milanovic (@milanmilanovic) May 28, 2019
I'm also encouraged by Milanovic's statement that T-Mobile 5G is "blanketing Manhattan." If that's the case, then T-Mobile is doing better at its millimeter-wave buildout than Verizon, which is currently focused on a 1.6-square-mile chunk in Chicago and a small area of downtown Minneapolis.
— Milan Milanovic (@milanmilanovic) May 28, 2019
There's Still a Lot of Mystery Here
T-Mobile hasn't announced a date for its 5G launch, for several reasons. The Galaxy S10 5G is still a Verizon exclusive, and will be until June 15, according to my sources. More importantly, T-Mobile will rely heavily on low-band 600MHz 5G spectrum, which that phone does not support.
The Galaxy S10 5G will only get T-Mobile 5G coverage where the carrier has millimeter-wave spectrum, which is a few major metro areas. (They just happen to be really important ones, like New York, Dallas, LA, and Atlanta.) T-Mobile's upcoming "nationwide" 5G will require newer phones with Qualcomm X55 modems, potentially including the upcoming Samsung Galaxy Note 10 late this fall.
T-Mobile's 5G strategy right now is also a bit of a mess because it's so yoked to the company's desperately thirsty desire to merge with Sprint. T-Mobile CEO John Legere has heavily promoted the idea that if the two companies merge, they will be able to provide superior 5G service by combining T-Mobile's mmWave and 600MHz portfolio with Sprint's mid-band 2.5GHz spectrum. That has meant de-emphasizing T-Mobile's solo plans.
We'll probably get to see how Sprint's approach works at the end of this week, as the company has said it's delivering its first 5G phones in four cities on May 31.
(Disclosure: PCMag and Ookla have the same parent company, J2 Global.)