What error message did you get with wvdial?

What is the content of your /etc/wvdial.conf file (without any account
or phone information)?

Here is a template you can use for /etc/wvdial.conf setup, just make
sure you have already symbolically linked your /dev/modem file to
/dev/ttyS0, and after you have it configured you should also make sure
that the it has the file attributes as follows:
-rw-r--r-- 1 ubuntu dialout 1248 2008-09-28 17:47 /etc/wvdial.conf
Note: the symbolic link should be:
lrwxrwxrwx 1 root root 10 2008-10-23 06:55 /dev/modem -> /dev/ttyS0
This assumes that your modem is detected at /dev/ttyS0, if not, try
/dev/ttyS1. Fill in the fields annotated as <> with the information.

To connect to ISP with wvdial command:
$ wvdial phone1
...etc
========================file /etc/wvdial.conf template================
[Dialer Defaults]
Modem Type = Analog Modem
Modem = /dev/ttyS0
Baud = 115200,N,8,1
SetVolume = 2
Dial Command = ATDT
Init0 = HUP
Init1 = ATZ
Init2 = ATDT;
FlowControl = CRTSCTS
Username = <>
Password = <>

[Dialer phone1]
Dial Prefix = 1
Phone = <>
Area Code = <>
Inherits = Dialer Defaults

[Dialer phone2]
Dial Prefix = 1
Phone = <>
Area Code = <>
Inherits = Dialer Defaults

ditto