No. It is mandatory that you have to use Jio sim card in JioPhone.
Yes, JioPhone does have a 3.5 mm headphone jack.
Yes, JioPhone does support the Gujarati language.
Yes, you can watch YouTube videos on the JioPhone.
JioPhone has 2.4 Inch QVGA TFT screen display. It has about 167 PPI ratio.