Your business will need at least one telephone line to receive customers' enquiries and so on. You'll probably need a business mobile phone too - particularly if you're going to be away from the premises a lot buying stock, attending fairs and auctions, removing and installing salvaged items and so on.
Internet access is vital. You're likely to use the internet to do things like browse for stock to buy, check out how much particular items are selling for, put items for sale on eBay, communicate with buyers and sellers by email and so on. You'll probably want a website for your business. You could use this as a simple 'brochure' with your contact details on it, or you could put your stock inventory, including photos, online. An e-commerce website will enable you to sell things online.
Make it as easy as possible for people to contact you. For example, if you'll be spending a lot of time away from your premises, consider keeping a mobile phone with you at all times. A smartphone with a data connection will enable you to pick up and respond to emails, keep up to date with your eBay listings, and check other things on the web while you're out and about. Make sure your phone is always charged and always on. Think about what will happen to unanswered calls. Make sure that callers can leave a message if they need to, and be sure to get back promptly to anyone who has left a message.
The telephone company will bill you every month or quarter for the calls you've made, plus an amount for the line rental for the next quarter. Website hosting and internet access companies will bill you monthly, quarterly or annually.
Various packages and discount structures are available to business users which can help to reduce telecommunications costs. Contact your telephone company's customer services department for details.