Nirmal - The only camera manufacturer I am aware of with a built-in 4G cellular modem is E-Line, unfortunately these cameras do not appear to be ONVIF conformant and only work with edge storage and their "cloud service". I doubt these will connect to any standard VMS platform.
Back as an integrator, I was doing some testing installing 3G/4G routers in Dotworkz D3 housings with PTZ cameras as they had enough room in the housing for it.
Have a look at at this unit from Brickcom Camera Search and Compare | Brickcom Corporation
Although this is not a DIY camera.
Are you looking to make a DIY camera with cellular modem?
Hi Jim - I am familiar with Brickcom but haven't used their cameras in any applicatioyes I have few big opportunities which prompted us to look for an integrated diy type solution
There are some pretty small modems you could put with a brick style IP camera in an outdoor enclosure...
or something else similar?
seems you could find a compact rugged modem to pair up with cameras and housing to create something easy to deploy... Good luck!