A method of operating a mobile terminal having a plurality of communication operation modes, comprising: determining a current communication operation mode of the plurality of communication operation modes; determining a current voltage of a battery that powers the mobile terminal; comparing the current voltage of the battery with a battery voltage threshold associated with the current communication operation mode; and changing the current communication operation mode to another one of the plurality of communication operation modes based on the comparison of the current voltage of the battery with the battery voltage threshold associated with the current communication operation mode wherein the mobile terminal has a plurality of call modes comprising: a Global System for Mobile Communications "GSM" 850/900 MHz band mode, a GSM 1800/1900 MHz band mode, a Wideband Code Division Multiple Access "WCDMA" mode, and/or a Voice over Internet Protocol "VoIP" over WiFi mode; wherein the GSM 850/900 MHz band mode has a battery voltage threshold V1 associated therewith, the GSM 1800/1900 MHz band mode has a battery voltage threshold V2 associated therewith, the WCDMA mode has a battery voltage threshold V3 associated therewith, and the non-call mode has a battery voltage threshold V4 associated therewith; and wherein V1, V2, andV3 are associated with maximum transmit power levels P1, P2, and P3, respectively, the method further comprising: comparing a current transmit power level with one of the maximum transmit power levels P1, P2, and P3 associated with the current communication operation mode; and reducing one of the battery voltage thresholds V1, V2, and V3 that is associated with the current communication operation mode if the current transmit power level is less than the one of the maximum transmit power levels P1, P2, and P3 associated with the current communication operation mode. determining a current communication operation mode of the plurality of communication operation modes; determining a current voltage of a battery that powers the mobile terminal; comparing the current voltage of the battery with a battery voltage threshold associated with the current communication operation mode; and changing the current communication operation mode to another one of the plurality of communication operation modes based on the comparison of the current voltage of the battery with the battery voltage threshold associated with the current communication operation mode wherein the mobile terminal has a plurality of call modes comprising: a Global System for Mobile Communications "GSM" 850/900 MHz band mode, a GSM 1800/1900 MHz band mode, a Wideband Code Division Multiple Access "WCDMA" mode, and/or a Voice over Internet Protocol "VoIP" over WiFi mode; wherein the GSM 850/900 MHz band mode has a battery voltage threshold V1 associated therewith, the GSM 1800/1900 MHz band mode has a battery voltage threshold V2 associated therewith, the WCDMA mode has a battery voltage threshold V3 associated therewith, and the non-call mode has a battery voltage threshold V4 associated therewith; and wherein V1, V2, andV3 are associated with maximum transmit power levels P1, P2, and P3, respectively, the method further comprising: comparing a current transmit power level with one of the maximum transmit power levels P1, P2, and P3 associated with the current communication operation mode; and reducing one of the battery voltage thresholds V1, V2, and V3 that is associated with the current communication operation mode if the current transmit power level is less than the one of the maximum transmit power levels P1, P2, and P3 associated with the current communication operation mode. comparing a current transmit power level with one of the maximum transmit power levels P1, P2, and P3 associated with the current communication operation mode; and reducing one of the battery voltage thresholds V1, V2, and V3 that is associated with the current communication operation mode if the current transmit power level is less than the one of the maximum transmit power levels P1, P2, and P3 associated with the current communication operation mode.