Can I connect to wifi but still use cellular? I would like to be able to connect to my cars dashcam via wifi while in the car but still be able to use my iPhone's cellular connection.  

The way the dashcam works, it appears as a wifi access point so the phone tries to connect to the Internet through it. How can I be connected to the access point while still using my phones cellular?
Actually this is possible!...

Use the following instructions:
1. Tap the blue arrow next to the name of the AirPort Express WiFi network to view more options.
2. Select "Static" as the type of IP address, and then enter the following IP address and Subnet Mask :

IP Address : 10.0.1.4 (for example)
Subnet Mask: 255.255.0.0

Make sure you leave Router, DNS, and Search Domains blank! This tells the iPhone that it should use its cellular network to route internet traffic rather than trying to do it via WiFi.