The cellular network operators in Montana are Verizon and AT&T. If you're a T-Mobile customer, then you can roam on AT&T's network in Montana. For example, T-Mobile prepaid customers get a 200 MB allowance).
However, I use MintSIM, and this T-Mobile mobile virtual network operator (MVNO) does not roam on AT&T in Montana.
[I have editing left to do here... I wish Ghost could save a draft of a post update!]
For the best service on AT&T network, get a phone that supports 3G Band 2 ("PCS") and 4G LTE Band 17.
Billings, MT Cellular Service
- ATT Mobility: I recommend supporting 3G Band 2 and 4G Band 17 for general use around Billings.
- 3G Band 2: Downtown (6 towers), Heights/Lockwood (4)
- 3G Band 5: Downtown (4), Heights/Lockwood (2)
- 4G Band 17: Downtown (4), Heights/Lockwood (2)
- 4G Band 4: Downtown (3), Heights/Lockwood (1)
Note: Supported Bands unknown for one Downtown tower.
Bozeman, MT Area Cellular Service
- AT&T Mobility: I recommend supporting 3G Band 2 and 4G Band 17 for general use around the Bozeman area.
- 3G Band 2: Bozeman (7 towers), Gallatin Gateway (1), Livingston (3), Bozeman Pass (1).
- 3G Band 5: Gallatin Gateway (1), Livingston (2), Bozeman Pass (3).
- 4G Band 17: Bozeman (3), Belgrade (1).
- 4G Band 5: Bear Canyon (1), Belgrade (1).
- 4G Band 4: Belgrade (1).
Note: Supported Bands unknown for four Belgrade towers.
Phone for use on T-Mobile and AT&T
- 3G Band 2: (1900 MHz, PCS A-F) is the band that T-Mobile and AT&T share, so you'd definitely want a phone that supports this.
- 3G Band 5: (850 MHz CLR) is only supported by AT&T.
- 4G Bands 12, 17, 5, 4, 66, 2, and 25 are used by both T-Mobile and AT&T.
Specific Phones Considered
Blackberry Priv STV100-1
- 3G UMTS/HSDPA:
- 1900 MHz (Band 2, "PCS") for AT&T and T-Mobile.
- 850 MHz (Band 5, "CLR") for AT&T only.
- 1700 MHz ("AWS") for T-Mobile only.
- 900 MHz ("E-GSM") and 2100 MHz ("IMT") for international use.
- 4G LTE:
- 700 MHz (Band 12, 17), 850 (5), 1900 (2), 1700/2100 (4) for both AT&T and T-Mobile.
- 700 MHz (Band 29), 2300 (30) for AT&T only.
- 2600 MHz (Band 7), 2100 (1), 1800 (3), 800 (20) for international use.
Adafruit FONA 3G (SIM5320A)
- 2G:
- PCS-1900 for T-Mobile only.
- GSM-850, E-GSM-900, DCS-1800 for international use.
- 3G UMTS/HSDPA:
- 1900 MHz (Band 2, "PCS") for AT&T and T-Mobile.
- 850 MHz (Band 5, "CLR") for AT&T only.
Updates
- MintSIM does not have the roaming partnership with AT&T that T-Mobile has, even though MintSIM resells T-Mobile service. So prepaid service with T-Mobile will get you AT&T roaming in Montana, but service with MintSIM will not.
- T-Mobile service may be expanded soon in Montana. See this and this.