Can i use Iphone apps to communicate to friends in other countries?

[Rooster.]

I am going on a long holiday soon and was wonder if i use apps such as Whatapp, MSN and Facebook. On my 3G connection would it cost me to send messages to my friends back in England though them apps ?
( would it use up more of my 3G MB's to send a message though an app )
( what about if i can get hold of a WiFi connection )

[Wonderfax]

You can use one of the free apps listed in the link below to find the password to wifi networks to give your free internet access!