Totally new to SIP/VoIP can anyone help me out?

[v1etnammer]

I understand that you can call using data rather than cellular air time but I was wondering about the finer details. I was looking at Fring and noticed two headlines which confused me. One said free calling, which stated that I can make free calls to my IM buddies but then it says that I can make cheap calls to landline and other cell phones using SIP or Skypeout.

Basically, I'm VERY confused and would really appreciate if someone could just give me a SIP/VoIP for dummies tutorial/manual of sorts. Thanks!

[ItemFinder]

Free calls means calls to other users online, just like Skype. To dial traditional landlines and cellphones, a per minute charge applies.

[v1etnammer]

Oh I see, that makes it slightly less appealing now :( lol most of my friends don't even have data plans. Thanks for clearing that up for me!