If your local carrier provides one of this bands in your area but you get no connection please check the APN settings. If this don't help please ask the Carrier-Service for help.
GSM Mode: EGSM900, DCS1800, PCS1900, GSM850
UMTS Mode: WCDMA-IMT-2000, WCDMA-GSM-900
LTE Mode (only for SIM1): Band 1,3,7,8,20