There are ways of selling goods and services on line without the visitor having to make a telephone call. Many people, these days, are perfectly happy to give their credit card details on line, providing a secure server is utilised to gather sensitive information.
In its basic form a shopping cart could be just a button or a hyperlinked piece of text that takes the visitor to an order page. The page will usually allow additional items to be added.
There are many commercial shopping carts that use templates and they can look very professional, but be sure to compare all the facilities offered before you make a decision. These solutions are ideal for a trader that has many similar items for sale and allow frequent updating and price changes. They also permit a high level of customisation to incorporate the house style of your website with logos and images etc.
You will need to have a bank merchant account in order to accept credit cards and they have very strict entry conditions which sometimes preclude smaller operators. In these cases why not consider using Paypal? This gives you a credit card facility without a bank merchant account and can be very cost...