I visited a client in April that had moved to new offices, but did not have a broadband service provider connection over xDSL. They had been given a USB device which you fit a SIM into and use the cellular network data connection for their access to the internet.
This is increasingly becoming a popular alternative, particularly with PAYG deals such as GiffGaff where you do not need to have a long term contract in place.
Many of the new routers coming out have the facility to have a USB 3G/4G modem attached to provide either a second connection to the Internet for data sharing, or a standby facility if the local broadband fails.
However take care
If you are using one of these devices, do check to see if there is a firewall included in the device. If there is no firewall you could be opening up your entire network to persons unknown on the internet.
A firewall is a protection device which will hide your local area network (your home, or office) from intruders attempting to gain access from the internet side of the connection. It performs several other local functions in order for your local area network devices to communicate with each other and the rest of the world.
There are also different classes of firewall. With varying levels of sophistication. In the ideal world you need a local firewall which performs SPI which stands for Stateful Packet Inspection. This means the Firewall is not only protecting you from the outside world, but is also monitoring what is happening on the established connections.
I could not say whether a USB dongle which provides 3/4G data connectivity does all of these things, however given that most mid to high end routers have a relatively powerful processor in them (enough power to be in a simple Personal Computer) it is unlikely that a USB dongle will provide this level of protection.
Solutions
If you have to use a USB 3G/4G data modem then it would be better to assume that you need a firewall as well. In fact a firewall/ router. This provides you with IP address assignment and other features which make your computers communicate. It also means you have some level of control over how your network is used and configured.
It could be an old router, that you plug into which was formerly used for broadband providing it can be configured for a 3G/4G data connection.
You could also use a local firewall on the computers in the office. I recommend looking at ESET Smart Security. I have used this for nearly 20 years on all of my Windows based devices. It provides an anti virus feature, and a local firewall. It also monitors what you are doing and blocks intrusions into your computer, and prevents access to websites that are not positively rated.
Conclusion
The bottom line is don’t blindly trust a data connection from the cellular network if you know nothing about it. Assume that you need some local protection to hide your local area connection. Your regular broadband router will do this for you, but a cellular network data connection over USB is very unlikely to be equivalent to your local router.