Another option is to use RaidCall, which is what I personally use for another game that I play. The resources that are required are 1/50th of Skype and I have not found any issues as of yet. There is also features to split groups easily which will allow for people to jump into different servers (Which are all hosted by RaidCall servers) depending on activity or who they wish to talk to. Another avenue of verbal communication to consider.
---Spamtron