Allow free SMS via carrier SMS -> Email gateways
Most cell carriers have an SMS -> Email gateway. This allows messages to be sent for free via email to any SMS number. This would be an alternative to requiring a cellular account to send SMS messages as they could be sent from the Skype network via an outbound email gateway. Also, it would eliminate the ludicrous 11¢ per message charge for outbound SMS with Skype credit. Google manages to support it via Google Talk for free so why can't Skype?