Are there specific frequencies used for voice vs. data? Or are all calls essentially data since they are digitized?

I ask because I have terrible reception (for voice) at home - calls drop completely or have frequent drop-outs.

I'd like to try a cellular extender but none of them cover every frequency supported by t-mobile and want to know if certain freqs are specific to voice (since wifi handles my data needs at home).

Extensive googling turns up nothing.