This app is only useful for phone with a Qualcomm chipset.
If you don't know how to add GSM / WCDMA / LTE bands to your phone, please refer to this thread: http://forum.xda-developers.com/galaxy-s5/general/how-to-add-rf-lte-frequency-bands-to-t2886059
That thread is for Samsung Galaxy S5, but the same principle is also applicable for many other phones, e.g. Samsung, LG, Sony, HTC, Nexus...
You also need some NV editor software (e.g. QPST, QXDM, EFS Professional...) on the PC to write these NV items to your phone.
>> NV items description:
+ Adding GSM / WCDMA bands:
NV 1877 (ID 01877) - RF Band Configuration
NV 0441 (ID 00441) - Band Class Preference
NV 0946 (ID 00946) - Expand Band Preference 16 to 32 Bits
NV 2954 (ID 02954) - Bits 32 to 63 of Band Preference
+ Adding LTE bands:
NV 6828 (ID 06828) - LTE BC Configuration
NV 6829 (ID 06829) - LTE BC Configuration DIV
Should you have any question, comment or suggestion, please do not hesitate to contact me on XDA: http://forum.xda-developers.com/android/apps-games/app-qualcomm-nv-calculator-adding-2g-3g-t2915649