Can I use the iPhone’s new “Assisted-GPS” out in the boonies? Or, does it NEED cell phone service?

I have a traditional GPS, and am really excited to get an iPhone that can replace it. But, I am afraid that the iPhone’s "Assisted-GPS" technology won’t work well once I’m out in the mountains. Is this as effective as traditional GPS?
If it does need cell phone service, then what makes this GPS different from the tower-triangulation the original iPhone had?

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