Based on information posted by Dan203 of the Tivo Underground.
The original post for this information can be found here:
http://www.tivocommunity.com/tivo-vb/showthread.php?s=&threadid=66115
Instructions
These instructions explain how to get a TiVo running software version 3.0 to use an external modem to make daily calls without any hacking or opening the case!
The modem is a US Robotics Sportster 33.6 but most external modems should work (US Robotics is recommended however). It's connected to the TiVos using the original TiVo serial cable and a RadioShack DB9 -> DB25 adapter. What has to be done to get it to work is shown below:
Connect the modem to a computer using the modems original serial cable.
Send the modem the following commands using hyper terminal, which disable DTR, RTS and flow control
AT&D0&H0&I0&R1&W0
AT&D0&H0&I0&R1&W1
Disconnect the modem from the computer and connected it to the TiVo serial port.
Flip the modem over and switch the "Terminal Override" dip switch to ON. (I had to do this because the TiVo would not connect to the modem otherwise)
Set the TiVo dial prefix to the following, including the comma:
,#319
Try to make a test call using the Tivo menus, it should work.
Try to make a daily call. It should also complete and finish successfully loading the data.
The connection speed is slow (i.e. 19,400), but it will successfully downloaded and index data. You can try a higher speed, such as 38,400, but it probably will complete only the test call but not the daily call.
Instructions for using HyperTerminal:
Open Hyperterminal.
It should pop-up a dialog asking you to make a new connection.
Just enter test into the text box and press OK.
On the next dialog select the COM port the modem is connected to, leave the defaults for everything else, and press OK.
You should now be connected to the modem, and have a blinking cursor.
More Modem Config Info
You may have to turn echo on to see what you type "echoed" on the screen:
ATE1
Not all modems may support all of these, but it may not matter - if you get an error, enter them one at a time with Dan's values:
AT&H0
n=0 Disable TX Flow Control
n=1 CTS
n=2 Xon/Xoff
n=3 CTS and Xon/Xoff
AT&I0
n=0 Disable RX Flow Control
n=1 Xon/Xoff
n=2 Xon/Xoff Chars Filtered
n=3 HP Enq/Ack Host Mode
n=4 HP Enq/Ack Terminal Mode
n=5 Xon/Xoff for non-ARQ Mode
(If your modem is not accepting &H and &I commands, try AT&K0 to disable all flow control.)
AT&R1
n=1 Ignore RTS
n=2 RX to DTE/RTS high
The AT&Wn justs stores as profile 0 and 1. The modem should power up profile 0, but this way it still works either way. The W0 is the factory default. You can set W1 to be the default after a power-on with the &Y1 command. Corrections or updates for this page: Note: Do not post questions, unrelated comments, or information of which your are uncertain. This section is reserved for corrections and updates only.
