We did at an old gig. Completely ditched the Indian offshore team for Mexico City. Generally, was a good experience, or was at least better than Tata/CTS/HCL.
The big changes were
- timezone overlap; they were Central Time and working for East and West costs weren't a struggle
- vaguely similar holidays / no surprises because no one in the US knows when Holy is
- level of English was usually better with the Mexicans, though they often had thicker accents; we could always find a Spanish speaker in the office if there were any communication struggles
- level of technical qualifications was usually better, in that Tata would be obligated to find someone who can do [X], and experience has shown that they'll find anyone, while the Mexican support teams usually had solid technical chops.
We had some limited success with a team in Argentina too, but there were a lot of tax and other logistical hoops. We had high hopes for the folks we reached out to in Brazil but they were never really organized, and I gather getting any sort of hardware into the BZ is expensive and complicated, plus they only have like 2 real Telcos and connectivity was problematic (this was like ~8 years ago, so things my have changed).