Severla Greek aothors later also mention this people, but they became more famous due to the corpus of inscriptions (about 25 at all) found in Southern Asia Minor and written in a special language. All inscriptions are too short and of the same structure, so the identification of the language is quite hard, but still it is believed to be one of the Anatolian languages, closer to Lycian and Sidetic. Probably Pisidic was a branch of Lycian, but as the tribe lived in an isolated place and rarely contacted with other nations, the language gradually acquired special independent features.
In the 1st centrury AD Strabo mentions Pisidia and its inhabitants already about 20 times. They were famous by their wary character (Herodot says they worshipped the god of war best of all), and it was hard for Persian, Seleucid and then Parthian invaders to conquer their lands.
Some element in the language is for sure Phrygian, and still another version is that Pisidic is a synthesis of Anatolian, Phrygian and aboriginal languages of Asia Minor.