Does data have priority over voice when making calls on 3G?
Voice and data are handled independently in 3G- voice uses circuit switching and data on packet switching. Hence, priority of one over another is not correct as claimed. For additional details see this

Frequent call drops could be due to other reasons like tower density, frequency used, congestion, Overloading etc, which can be addressed by your carrier. Your signal can be strong, yet you may face call drops or not being able to connect because of these issues