My suggestion, power everything down, swap and power up. If all works, you are done. You may be able to replace the equipment with no changes.
A modem by itself has little to do with Obi configurations. That is unless there is built-in router too.
The router should be configured the same way as the old one (SIP-ALG off if that was off before, but recommended as off anyway).
If you used DHCP to vend IP addresses, then make sure that is on.
If you hardcoded an IP address for the Obi, make sure that you do that again. The same holds true if you enabled Quality Of Service.