Skype this past week indicated that there has been a delay in getting their Skype Mobile up and running.
While they have been delayed other options have been popping up. For months PhoneGome has had the ability to bridge a call between the mobile phone and the VoIP world. Another entrant is iSkoot which made the news via David Gardner's article in Information Week with a software update that supports dual mode phone calling over mobile of WiFi connections.
Another entrant is Fring, whose founders and backers have roots in ICQ. I met them at VON in Boston.
All these options that seem to be emerging are there without carrier cooperation. In some cases, as Gardner points out, they won't work, as in here in the USA over Verizon Wireless or Sprint's EvDO networks. Until there is carrier cooperation, don't expect much growth in these service areas. Data network adoption rates are not nearly as prevalent as voice plans, and many people don't even know that they are available.
Mobile Ignite, a trade organization I've been asked to advocate for recently passed a new specification. That spec makes the concept of a seamless handover between WiFi and GSM networks similar to a standard. The spec is pre-IMS compliant and will also be IMS compliant. This is key because, as the release states: " A key goal of the Functional Specification was to ensure that dual mode cellular/Wi-Fi handsets that perform handover on current networks will not need to be modified or replaced when the network evolves to IMS, and becomes compliant with the VCC standard – and can continue to operate with no impact to the user. This removes the risk for handset manufacturers and service providers to deploy SIP based handover capable dual mode handsets for use on current networks and accelerates the market for FMC Handover services."
Alec Saunders has some thoughts on this issue also.