In telephone conversations, transmitted speech of good to excellent quality is desired for enhanced Quality of Experience and to sustain lasting customer loyalty. Subjective mean opinion scores account for perceived transmitted quality, while instrumental models, such as POLQA, are able to estimate the subjective judgments. To perform subjective or instrumental quality measurements, the International Telecommunication Union recommends to employ two sentences from both, male and female speakers as speech material. In this paper, we have examined whether subjective and instrumental MOS ratings are affected by perceptual voice likability. A listening test has been conducted over 8 degradations with 12 extremely likable and unlikable male and female speakers. Statistically significant effects of gender and of voice likability have been detected on subjective MOS, whereas instrumental MOS was only affected by gender differences. These results can contribute to further improvements needed in the POLQA perceptual modeling, as well as to the selection of speakers for speech quality assessment tests. © 2018 IEEE.