Hi Hector,
Can you be specific about what you want to use 4G for? Protection of a connection between a central site and a remote branch?
Details of WAN bandwidth requirements are detailed in the UCM SRND, you should use those for guidance. Ultimately, you'll need to be confident about the minimum throughput level for the 4G connection and whether this will be sufficient to meet the traffic load during failover.
Ultimately the WAN technology is less important that its reliability.
Cheers
Andy
