A question about the Wi-Fi (WLAN) and VoIP in the new phones Nokia phones.

They use Wi-Fi is 802.11g and Nokia promises you will be able to make VOIP calls over Wi-Fi. Do you need a business VOIP system (PBX systems from Cisco or Avaya) to make VoIP calls then. These phones are business VOIP solutions, not Skype consumer phones - right / wrong?

Nokia has said it will launch VoWLAN or hybrid phones for business use - is it the Eseries they were talking about? I getting confused with the all these techniocal terms and then they have several terms for one thing (like WLAN and Wi-Fi etc.).