How are the gain and corner frequencies calculated for this speech bandpass filter?
The main part of the filter (sectioned in red below) is a modified MFLP filter and not a Sallen-key filter: -



I've used Mr. Okawa's web site for doing the analysis and it tells me that the cut-off frequency is about 3.2kHz and there should be no peaking because the Q (or damping ratio if you did the math) is about optimum for flat response (\$\frac{1}{\sqrt2}\$).

The high pass stage is at the input with C1 and R2//R3. This works out at 318 Hz for it's 3dB point.

One slight modification to the general type of circuit is the 2nd op-amp (that forms the MFLP filter) receives mid-rail bias from R2 and R3 but also a smidgin' of input signal. This doesn't alter the frequency response too much but does subtract 1 from the calculated gain of the 2nd stage. Okawa calculated it at 10 when I believe, with the modification it will be 9. The first op-amp stage gain is 11 and the total gain (at mid-frequency)  will be 99 and not 100!