A dial-up internet connection uses up the phone line. During internet use the line is not available to make or receive phone calls. If you wish to be able to use the internet and talk on the phone at the same time you should look into getting a second phone line for the internet and have your first phone line for phone calls.
Another option that may be available in your area is DSL. If your Internet Service Provider (ISP) has DSL service in your area and it is affordable I would recommend it as it is often fast than dial-up and can allow you to still make phone calls over the phone line, provided filters are installed to remove the DSL signals before they reach the phone.