I am not quite sure what you mean by "machine with mobile internet connection". I think you are referring to the use of one of those devices that you can plug into a laptop or desktop computer that will give it internet access using a radio link to a cellular phone service provider, but I could be wrong.
It's very hard to provide public access to computers over such a link. That is because the IP address of the machine is often not a public IP address, but instead a DHCP-assigned address from one of the internal address blocks, which, unlike public addresses are not unique.
Even when you do have a globally-unique IP address, however, the mobile internet service will often have a firewall set up to block that address from serving.
So you may have to select an alternative Internet Services Provider and hardware.
Customer surveys are for companies who didn't pay proper attention to begin with.