For a few years now, GNSS observation data of Android smartphones are readily accessible. In this paper, code and carrier-phase observations of three different smartphones (Xiaomi Mi8, Huawei P30, and Samsung S20) are analyzed with respect to availability and quality. For applications under favorable environmental conditions, position determination with an accuracy of a few centimeters is feasible. A prerequisite is that the carrier-phase ambiguities have integer property. Smartphone antenna calibrations revealed that for cm-accurate positioning, at least the phase center height offset must be taken into account.