Is it using data on a local free wifi with iPhone?

I'm traveling to Mexico City for 10 days Starting this Friday. I was struck by huge cell phone bills in the past ($ 600 from Guatemala, ouch!) when traveling abroad. However, this is my first time with my iPhone. Can I use Wi-Fi instead of my local 3G network to avoid charges? Will I be able to surf the net, check e-mail, and especially the free use of Skype in this way?

As long as you do Fi, you will not load. Keep the phone in airplane mode unless you know you're in a wifi hotspot.

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