Software like MobileTalk from Packet8 would help, but it is bound to just one VoIP provider and could be done much better. Unfortunately the underlying software from Mobilemax gets distributed only to companies and not to end users. So people have to wait until their VoIP provider of choice implements it.
But salvation is near, at least for iPhone users: RingFree let's you use every VoIP provider or even your own Asterisk / SIP server for outbound calls on Apple's "Invention of the year 2007" (according to Time Magazine). iPhone Atlas has the story:
Here, in a nutshell, is how the app works: A user registers with RingFree, entering his iPhone number and providing some other information. The user is then prompted to call a country-local number to confirm their information by entering a PIN. Once logged into the site, the user selects from a list of pre-defined VoIP providers (including VoicePulse, Gizmo Project, PhoneGnome and others) or defines his own by entering a proxy address, username and password.
RingFree is basically a website with a virtual dialer. It is linked to VoIP providers of choice and uses standard voice minutes to make VoIP calls. Therefore it doesn’t require any hacking or jailbreaking, nor does it require the presence of a WiFi network. Only a small amount of data is transferred over the EDGE network to signalize the call. The voice quality is reportedly good, and calls go through without too much delay so that a commentator at IntoMobile states:
Thank you for this. This is the most useful iPhone application yet. I set it up in less than 2 minutes and I made a call to Ireland using Gizmo Project. Sweet and simple. I am happy and would be jumping up and down with joy if it let me call Skypers.
That's exactly what I was looking for. RingFree is free in the first month, then it costs $30/year. You can also call Google Talk, Yahoo or MSN contacts from the iPhone. I wonder when someone will launch a similar service for other platforms, such as Symbian. It could be a great new feature for Voxalot, whose mobile callback I often use with my own VoIP providers. It costs €0.01 of data or less to establish the call, but still it demands two simultaneous phone calls.