Does anyone knows if I can send SMS text messages to Mexico from my iPod Touch?

I don’t see a problem with this providing you have the software or the website your using ready. The location really shouldn’t matter.

If you happen to know the provider of the person you’re sending text messages to, you can check out their website and see if they have an email-to-sms program. A lot of carriers provide this service for free (some don’t, so beware), and it essentially allows you to send an email to your friend AS the text message to a special email address specified by their carrier (e.g. 6045551234@mycarrier.com).

Verizon allows you to send a text from their website

I’m not sure about other carriers, but you could check.