[Subrata Jana]

I am facing crucial problem call dropping in my Lumia 640XL. is it problem of handset?

[Jazmac]

Might only be a problem with your carrier. Take it in and have them update your sim card.

[Subrata Jana]

Sim is new. My friend also using the same sim Card in android. They did not facing the problems.

[Chintan Gohel]

I am facing crucial problem call dropping in my Lumia 640XL. is it problem of handset?

call drops are almost always an issue with telcom network issues. But you can also check that the SIM if firmly in the slot of the phone

[Jazmac]

Sim is new. My friend also using the same sim Card in android. They did not facing the problems.

You can't just go by the appearance of the sim. It is how the sim was programmed at the telco. Its not an unusual problem so its best to check with your telco.