I have had just one experience of dongles - bad. I bought it to work in a specific place, but that place had no coverage. I did get my money back.
Three friends of mine have dongles, and they all give me very good reports. One ha a slingbox at home so she can watch her own tv and recorded programmes on her laptop whilst she is away - the speed is usually, but not always, fine for that.
I would recommend Skype for your needs - it would cost you nothing except the handset/headset.
This is a typical handset:
http://www.lambda-tek.com/componentshop/index. pl?origin=gbase18.2&prodID=B94513
I haven't used one so don't know if they are any good.