So my sis was talking about getting a pda phone since she's a new resident at a hospital. I wanted to get her a pda phone; she was looking at the hp ipaq hw6940 or hw6945. She was mostly concerned about this supposed voice over wifi thing that some people do at her hospital where they don't use minutes to talk over the wifi network? I recently got several tmobile wings with a fam plan and was wondering if they can be used for the same thing instead. She said she saw someone with the hp ipaq that can do the voice over wifi thing. Can someone explain what this feature is and which phones/networks can support it? Thanks a bunch in advance!