Make sure the modules for the modem are loaded with "lsmod". Look for the name of the driver in the list of loaded modules. If it's not there try loading the module with "modprobe module-you-want-loaded".
If you see the module use "dmesg" and look through the messages there to see if you see your modem being enabled, or if there are any errors when it tried to load the modules.
If the modules are loaded try "wvdialconf /tmp/wvdial.conf" which will autoprobe any modem it finds and let you know if it's working. If this doesn't find your modem it is probably not loaded, or is loaded at a really f'd up placed.

I wish I could help in more detail, good luck. Winmodems are a pain the the arse
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