Possibly a pretty basic question, but I'm not sure. The installation tech said that I had to use their router, and installed one of the 2wire ones - a i38HG one. It's fairly slow and poky compared to the one I used to use with comcast internet - a netgear WNDR3400. Is there any way to use the netgear one instead? Can I just switch the network cable from the 2wire to the netgear router and make it work somehow?
The i38HG is not actually the router, it is just a break-out box that supplies 4 Ethernet ports and a wireless access point.
The actual router is the i3812V unit (the iNID), which is outside attached to your house at the phone line entrance.
You can put your own router in the house to replace the i38HG, but you will have to run an Ethernet cable from that location to the i3812V. The i3812V has an Ethernet port in the outside unit that can be used for this. By default, it's not enabled, you will have to turn it on in the router interface:
You will also need to keep the i38HG around and handy. Since the Ethernet port in the i3812V defaults to disabled, if the outside unit ever loses power or is factory reset, you will need to go back into the web interface to re-enable it. The only way in at that point is through the i38HG.
Once you have enabled the Ethernet port and run your Ethernet cable, set up your own router using the instructions here: