Emergency 911 Using a USA-based Phone

[MissMyBike]

I have been wondering that in case of an emergency, whether calling 911 from a USA-based mobile phone, while here in GTO, would ring the local emergency services. Moreover, would such a call require certain codes to make the call go through? Thinking about it, this is probably a circumstance affecting any US-phone user, traveling anywhere through Mexico.

I'm guessing it is not a good thing to call 911, just to find out! Any advice would be appreciated.