If you are waiting for Skype client on Symbian you probably should suspend your hopes until arrival HSxPA or other next-generating networks. Skype still not release it's client for Symbian. As we know only phones run Symbian so Skype don't ready to play on this field. In the meantime there are a bunch of third-party solutions that transfer voice over current cell networks to the Skype network. Such well-known solution is Fring free VoIP client software that actually encode voice with AMR codec and transfer it to its server.
But I think Skype is losing to traditional VoIP clients in consumer phones. There is a lot of free SIP VoIP clients for Symbian even embedded into phones like in Nokia Internet Edition devices N80, N73 etc. If Skype will waiting too long it might completely lose this battle to companies like Betamax (VoipDiscount, VoipCheap brands).