Yes, Samsung HM1350 comes with volume control buttons.
Yes, you can conenct 2 mobile phones with Samsung HM1350 bluetooth headset.
Yes, you can connect with Vivo Mobile.
To connect Samsung HM1350 with your smartphone, please follow the below steps.
01) Make sure that your smartphone's Bluetooth is switched ON.
02) Switch ON your Samsung HM1350
03) Now search for the visible devices on your smartphone
04) select Samsung HM1350
and you're done.
No. It does not have.