We have just published public phone numbers for USA and France. Granted, telephone isn't new or even high-tech and there was actually no good reason for Lokad not to support customer phone calls right from the start. Yet, better late than never.
We are currently relying on a small call center setup based on Skype and PrettyMay. It might not be suited for large companies, but if you don't to need to handle more than 30 concurrent calls, then this is definitely a nice solution.