Advice needed with skype vs voicenet

[stomm]

Hello everybody!

I've got moderate experience using Skype but a gent who i work with uses voip to speak to his brother all the time in Fiji.
(edit : though it was NZ sorry!)
He's got an old PC connected via ethernet to a dsl modem (NTL broadband). Sometimes his call to his brother can have 5/6 seconds delay, and for his calls he's paying anything up to 120 quid a month - i said that i believe with a router and a wifi voip phone life should be a lot easier for starters.

He explained though that his brother is on voicenet (a company i've never heard of) but he personally uses skype. If we find a voip phone and router to buy, can you contact users outside of skype (but still on voip) or should i go down another route.

Thank you very much in advance, please don't hesitate to give me a shout if this doesn't make much sense.