Holland’s Nimbuzz, another mobile app that hopes to aggregate all kinds of messaging networks and VoIP services, has raised a $15 million second round to add Windows Mobile, iPhone and Android support to its list of 23 currently supported mobile operating systems. The round is led by South African media firm Naspers’ Myriad International Holdings (MIH) digital arm, which is joined by Luxembourg-based Skype backer Mangrove Capital, which gave Nimbuzz its $10 million first round along with Holtzbrinck Ventures in June 2007.

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Seventy-employee Nimbuzz gives access to a sometimes confusing array of protocols like Skype, AIM, Yahoo (NSDQ: YHOO), MSN and GTalk and has competition from the likes of Fring, the UK’s Trutap and, of course, the individual mobile products offered by social networks and VoIP services themselves. It says it has involvement from 10 social networks,  has lined up carriage from three mobile operators and has over a million registered users at a rate of 5,000 signups a day.