It depends how the freemium offering fits into your business model.
If you see free as the top of the funnel for customer acquisition, then you should provide lots of customer support.
Leading companies might offer phone support, online chat, and email, in addition to more cost-effective tools like user forums and FAQs. More importantly, they see customer service as a sales and marketing tool, rather than simply a cost center. This means that the people handling calls and chats know how to upsell callers, rather than being focused purely on solving the problem that generated the call in the first place.
If, on the other hand, you see freemium more for awareness or as a tool for viral growth, investment in customer service may not be justified.
Some companies make live support available, but hide the access points, making it difficult for the average user to find the phone number or link to connect to a person. While this approach might be interesting from a testing perspective, allowing the company to see if users who have a live experience are likely to upgrade, companies using this approach risk losing potential upgraders, by making it too difficult for them to solve their usage problems.
Any company thinking about what kind of support system to set up for their new offerings should track results and know what their objectives are. Users of free services are generally understanding of the fact that they don't get the same level of customer support, but just because users don't demand support doesn't mean that providing live help won't make a measurable positive impact on revenue.
