Hello- and welcome to the forum.
Until just very recently, I had been totally confined to using old fashioned dial-up. Though my modem is a pci slot full hardware modem and not connected via USB, the basics should work the same. The fact that you can talk to the modem via minicom shows that the hardware is all working just fine.
I'm not entirely sure how to interpret your statement: "What I am unable to do is to get the computer to answer. ".
I can only assume you mean dialing in to your ISP account, which I also assume, you have setup. I have found that for configuring dialup, using "system-config-network" works best and is the easiest. If you don't have that installed, then:
su -c 'yum install system-config-network'
Or just use your package manager if you're more comfortable with that. Look for "Network" in your menu after you install system-config-network, or just bring it up from the command line, as root. If it doesn't already find a "Modem" device, just click New while on the Devices tab, then select Modem connection. You can setup everything you need using just the Devices and Hardware tabs and their sub-tabs, including entering your ISP info (username, password, phone #) and doing the Edits as necessary for the new modem device you're setting up.
Uncheck the "Controlled by NetworkManager" box
Check the "Allow all users to enable and disable the device" box
Hope this helps.
---------- Post added at 08:09 PM ---------- Previous post was at 07:56 PM ----------
I realize also, that you may very well mean "the other computer to answer", and not an ISP account. In that case, that adds the complexity of.. "is the other computer setup correctly to have its modem answer on ring?".