Using Mobile VoIP over 3G Cellular Data
The use of Mobile VoIP over your mobile phone's data connection raises several very important issues.
(1) The Need for a Flat-Rate Tariff Mobile Data Plan
For mobile VoIP to be economic you need an unrestricted flat-rate tariff data plan on your mobile similar to the low cost flat-rate plans available to landline users that have been instrumental in the success of fixed line VoIP.
The mobile industry has only recently started to move towards suitable flat-rate mobile data plans.
Skype and others have given the lack of suitable data plans as a reason why they have not yet made a big effort with mobile VoIP, expressing concern that though they can claim their part of service is free or very low cost, the mobile user was likely to be hit with very high mobile data use fees. (There are also technical issues for Skype.)
Even if you have good Data Plan for use in your home country you may find that the tariff when you are roaming makes it very uneconomic for Mobile VoIP or for international calls.
(2) A Mobile Data Plan that Allows VoIP
Even though attractively priced flat-rate mobile data plans are becoming available, mobile service providers are placing restrictions on their use for VoIP and other services which they believe constitute unfair use.
For example, Vodafone specifically excluded VoIP services such as Skype and peer-to-peer services such as instant messaging and file sharing from its new flat-rates for data. If these services are used they will incur higher charges including a minimum charge for a data session.
Other service providers in varying degrees are imposing fair use conditions. Even those that appear to allow greater freedom word their terms and conditions so that they might exert more control as usage patterns unfold.
(3) Quality
Though VoIP quality in general can be noticeably better than the voice quality found on the PSTN and mobile voice networks, it is not possible to rely on it yet.
VoIP suffers from unpredictable delays and other problems, making it a best-effort service, and established mobile operators have put this forward as one of the reasons they ban or discourage VoIP. They do not want users to feel let down when they are used to the reasonable quality and great reliability delivered by 2G/GSM and 3G mobile voice networks.
At this stage of industry development it seems Mobile VoIP might be fine for everyday social calling especially amongst friends but could be disappointing if used for business where any poor quality or unreliability could be a big nuisance.
You need 3G mobile data. 3G data is also in the process of being upgraded to higher quality and capacity data services. Mobile VoIP over 2G data (GPRS) hardly works.