http://www.htc.com/us/smartphones/htc-one-m8-windows/
2G/2.5G - GSM/GPRS/EDGE:
850/900/1800/1900 MHz
3G - WCDMA:
850/900/1900/2100 MHz with HSPA+ up to 14.4 Mbps
CDMA:
800/1900
4G - LTE:
Bands 3,4,7,13
http://www.htc.com/uk/smartphones/htc-one-m8/
2G/2.5G - GSM/GPRS/EDGE:
850/900/1800/1900 MHz
3G - WCDMA:
850/900/1900/2100 MHz with HSPA+ up to 42 Mbps
4G - LTE:
800/900/1800/2600 MHz
http://www.htc.com/us/smartphones/htc-one-m8/
2G/2.5G - GSM/GPRS/EDGE:
850/900/1800/1900 MHz
3G - WCDMA:
EMEA: 850/900/1900/2100 MHz with HSPA+ up to 42 Mbps
Asia: 850/900/1900/2100 MHz with HSPA+ up to 42 Mbps
AT&T: 850/1900/2100 MHz with HSPA+ up to 21 Mbps
Sprint: 850/1900/2100 MHz with HSPA up to 14.4 Mbps
Verizon: 850/900/1900/2100 MHz with HSPA+ up to 14.4 Mbps
TMUS: 850/AWS/1900/2100 MHz with HSPA+ up to 42 Mbps
CDMA:
Sprint: 800/1900
Verizon: 800/1900
4G - LTE:
EMEA: 800/900/1800/2600 MHz
Asia: 700/900/1800/2100/2600 MHz
AT&T: 700/850/AWS/1800/1900/2600 MHz
Sprint: FDD 800/1900 MHz , TDD 2600 MHz
Verizon: 700/AWS/1800/2600 MHz
TMUS: 700/AWS MHz
http://en.wikipedia.org/wiki/List_of_LTE_networks