In our case, we offer 24/7 web chat support, a ticket system, and a forum.
Personally, the best way of providing support is by creating a forum. Not only it creates harmony between the visitors and the administrators, but also, it promotes a website's growth.
A web ticketing system such as zendesk.com or freshdesk.com will easily do the trick. Phone support is usually unnecessary and costly, but if your competitors are providing it, you may need to as well. Usually a skype account and phone number will work just fine.
24/7 chat IMO is unnecessary as well as customers usually prefer either the email / phone route.