Today I finished the "mobile VoIP experience" (surviving with a cell phone without voice plan, only w/ Internet). I wanted to end it before, but the telco had refused to convert my data-only plan to a voice+data plan -- until today, when I threatened to cancel the subscription. The power of --force.
In a nutshell, using MoIP is still too painful, not usable at all by a non-nerd. It worked, it may be useful for an emergency, but data networks must improve a lot until it gets "usable".
The main tool which I used to survive meanwhile was Fring, which is a wonderful piece of software. Apart from messaging capabilities (for which I will continue to use Fring anyway), the best combination of VoIP was Vono (a Brazilian SIP VoIP service provided by a mainstream telco, GVT) and Fring. Fring's Skype gateway does not work so well for voice.
For example, I could keep a conversation using Vono even over EDGE. Skype didn't go well even over 3G. Fring compression makes voice difficult to understand in noisy environments, and that seems to compound with Skype compression too.
The best thing would have been to use the SIP stack shipped with the Nokia N85, which has a reputation of being good and easier on the battery. But it has a simple and crucial problem: it does not do access point handover easily. It would tie me to use either WiFi or 3G, while Fring exchanges back and forth automatically, giving preference to WiFi if you want. The sad thing is that probably Nokia will not make its SIP VoIP work so transparently because it would hurt some telco's feelings.
Of course, MoIP over WiFi works very well, as Skype works well on PC. If you work and live in areas with WiFi coverage, the chances of surviving with MoIP are higher. Just connect once to every WiFi spot, so it becomes a registered access point and Fring will use it whenever possible.
I expected better service from 3G. Even in 3G and 3.5G areas, phone calls over Fring are difficult. Several reasons add up to cause this. Brazilian 3G is still in development. Telcos are providing a suboptimal service. 3G is not as good as we might expect by reading the theoretical specifications, bandwidth etc.
And finally, it seems that a large percentage of Brazilians get a 3G data plan and actually use as a primary Internet connection, and the thing was simply not engineered for this usage pattern, which disrupts service for uses like me that desire a very small but reliable bandwidth for MoIP.
I have made some tests and the biggest problem with (local) 3G Internet is the bandwidth variance, from absolute zero to twice the contracted bandwidth! At least, 3G works well enough for other applications like Google Maps which fetch maps as they go.
Another reason for using WiFi is battery life. Fring is known to drain batteries fast. Actually, I think the culprit is the always-on data connection, either WiFi or 3G. At least with WiFi it endures 24h or more. With 3G it lasts 6-8h. Using the phone in a completely c00l way (GPS + Google Maps + Fring + music player), don't expect it to last more than 3-4h. Anyway, if someone had a software answer for this particular problem, would easily grab a couple Nobel prizes :)
