TmoNews is reporting that some unlocked iPhone users may be picking up T-Mobile's 3G network in small areas of the Pacific Northwest -- specifically limited pockets in Nevada, Utah and California -- due to spectrum reallocation under the 1900MHz band.
Most unlocked iPhone users are relegated to 2G due to most of the T-Mobile 3G network running on the AWS spectrum of 1700MHz/2100MHz. We're not exactly sure what they're reallocating the spectrum for, however, multiple reports have surfaced from Howard Forums detailing a jump in speeds and, more specifically, the 3G network indicator popping up in the statusbar on their unlocked iPhone.
It's possible that T-Mobile could be testing spectrum allocation for new devices or simply to expand their network range for existing devices that already support the 1900MHz band, but again, there's no concrete evidence on what precisely they're up to. If you're lucky enough, however, you may be able to hop onto their 3G network depending on the area you're in.