Sending a message trough modem.

[xanatose]

Is there any program that could let a voice modem to call my cell phone whenever the internet is down or the computer is running on battery backup?

[dedndave]

that doesn't sound too difficult
although i don't know of a program out there that does what you want, i am sure they exist
i am not so sure about how to talk to a modem under windows, though
with win95/98, you could issue a set of AT commands and the phone number and it would dial it

[Tedd]

I'd start here.. (TAPI - Telephony API)

http://msdn.microsoft.com/en-us/library/ms811409.aspx

[ecube]

an alternative is simply write a program using WMI or wathave you that detects when your computers battery is low then send your cell phone a text message. Alot of people don't know this but you can send just about any cellphone thats using a major carrier a text message using your email.
its usually cellnumber@carrieremail.com heres a list to get you started. http://allthingsmarked.com/2006/09/04/howto-send-free-text-messages-through-email/

[ZhanZongru]

Which type of Modem do you have?
I have written a program to use a Serial port GPRS modem to for sending SMS and calling.
It is not very difficult, for there exist a bunch of free AT Command library on Internet in public domain.