I'm using this thread to share my own problem. I just received my rasberry pi kit today from pcwzrd13. I've had the no dial tone error and that has changed to No Carrier.
I should mention I don't have another dreamcast modem to test with and I don't have a multi-meter like support recommends.
What I do have:
I have two green lights on the USB modem and 1 red light on the raspberry pi.
Multiple phone cords that I have swapped and that has not made a difference
I have an Obi200 VOIP adapter, which provides a dial tone for my 2.4Ghz cordless phone. It essentially mimics an active phone line. I have used this to connect the dreamcast instead of the raspberry pi to test if my dreamcast modem is working. With this connection, the error is always, No Answer, No carrier.
I am using the Sega Dreamcast Web Browser (pretty sure it is the original, not 2.0). I do have Quake III somewhere if you think I should try that.
When I first started connecting, I had the no dial tone error immediately. Nothing I did seemed to change that.
Just recently, I configured the DMZ on my router and now the error I get is No Answer, No Carrier, which takes about 30 seconds.
I didn't think changing the DMZ would affect anything for the connection, but its now a different error.
I am using wifi and have not tried to use Ethernet yet.
The dreampi does show up on my network router with a good connection.
Web Browser Settings:https://imgur.com/a/so0lTwA
Dreampi dhcpcd error?https://imgur.com/a/mnv7dGN
Obi200 connection test (no Dreampi involved)https://imgur.com/a/cwarrca
Dreampi No Dial Tone Errorhttps://imgur.com/a/OS3v5HO
Dreampi No Answer, No Carrierhttps://imgur.com/a/NefXd8f
I'm not sure what to do now. I used to be a lot better at this 15 years ago...
I don't mind buying another LVI or DC modem to try and make it work.
Just wondering what the community thinks.