Although T-Mobil USA wrote in the September letter to customers that they were “interested in offering all of our customers a no-compromise iPhone experience,” the fact of the matter remains that the carrier’s network bands are not supported on the iPhone 4S.

T-Mobile’s 14.4 HSDPA (High-Speed Downlink Packet Access) GSM/UMTS network operates on the rather odd 1700/2100MHz frequency bands that are incompatible with iPhone 4S and other UMTS phones supported by standard 850/900/1900/2100MHz bands. However, some unlocked iPhone users are detecting 3G signals on parts of T-Mobile USA’s network utilizing the 1900MHz bands, according to

Nevada, parts of Northern California and the Pacific Northwest are also seeing some pockets of 1900MHz spectrum refarming for HSPA+. There are other parts of the country T-Mobile can refarm the 1900MHz spectrum but, the focus is on the Pacific Northwest, Nevada, Utah and California for right now from what we’re told. We should emphasize and emphasize greatly that this post does not mean that all of the aforementioned areas are seeing this refarmed spectrum, just pockets inside those areas.

A thread on T-Mobile’s support forums indicates that a carrier support representative told a customer on Oct. 14 that an “unlocked iPhone 4S will work on T-Mobile with speeds up to the max of the iPhone’s capability, using the UMTS 1 (HSPA+, 2100MHz) band of the iPhone”. Theoretically, should T-Mobile roll out the HSPA+ 1900MHz spectrum across the rest of the country, they could carry the iPhone (if Apple green lights such a deal). The main ‘minor’ drawback: It would only support T-Mobile’s 3G speeds. If you want to take advantage of this, and live in one of the areas with 9100MHz pockets, simply purchase an unlocked iPhone 4S. Pop a MicoSIM from T-Mobile into the unlocked smartphone, activate it, and you are good to go.