I experience connectivity issues quite often while using internet.
Most of the times the internet connects with 4G and after using for a few minutes the connection changes to Edge/GPRS untill I reboot the device.
However, the voice call quality is nice overall, no call drops experienced.
PROS:
Nice call quality.
Wide network access.
CONS:
Expensive
Internet conectivity issues
Higher call and data charges as compared to other carriers