or wonder why about this:
according to the US department of state there is going ot be New Requirements for Travelers to and from the Caribbean, Bermuda, Panama, Mexico and Canada.
A passport or other secure, accepted document will be needed to enter or re-enter the United States by december 31, 2007 - Requirement extended to all land border crossings as well as air and sea travel.
http://travel.state.gov/travel/cbpmc/cbpmc_2223.html
"This is a change from prior travel requirements and will affect all United States citizens entering the United States from countries within the Western Hemisphere who do not currently possess valid passports. This new requirement will also affect certain foreign nationals who currently are not required to present a passport to travel to the United States. Most Canadian citizens, citizens of the British Overseas Territory of Bermuda, and to a lesser degree, Mexican citizens will be affected by the implementation of this requirement. "
but note and worth repeating "to a lesser degree, Mexican citizens will be affected by the implementation of this requirement"
Historically, it's because Alexander Graham Bell was a dual national of the U.S. and Canada. The U.S. and Canada are the only countries that share the same international dialing code ("1"). The old Telephonos de Mexico -- when it was a state-run operation used a mix of Seimans and Western Bell switching equipment (most Latin American countries did the same -- they didn't want to depend on any one country for vital imports). Under the privatized TelMex, the system is changing over to standard Western Bell switches, compable with those used in the U.S. and Canada.
And, then too, a lot has to do with rate structure and international agreements. We still have outrageously high phone rates, but they're coming down, and the service is improving tremendously (one advantage of a crappy infrastructure is that when it finally is replaced, you get the newest and bestest!)