Having just gone through the unlock process...

TMobile has a policy where they won't unlock a phone unless you've been a
customer with that phone for 90 days; its not that you must wait 90 days from
the day you request the unlock.

If you've been a TMo customer for 90 days with the phone you want to unlock,
you shouldn't have much problem with the request. As others suggested, I'd go
through the web page.

Good luck
Chad

Another route would be to buy a cheap nokia 3390 or 5190 off ebay and use that
while in Mexico They are simple to unlock with codes found for free from the
internet, and many times are unlocked already. Plus you will always have a
backup in case your good phone goes belly up or missing. I would avoid any
cheap motorola phones. You can find them real cheap but the battery life is
usually terrible. Not worth the effort.

George

I just returned from a family trip to Cancun. We needed to coordinate 3
separate groups arriving at different times, from the moment they hit the
ground. Rather than pay international roaming rates on all phones I
decided to give local prepay a try. We did this last year for a trip to
the Philippines and it worked out extremely well, so I was willing to try
again in Mexico. Due to the need for having phones active from the moment
we hit the ground, the only choice was to pre-buy prior to departure. I
chose Cellular Abroad, who delivered an active SIM with phone number well
in advance of departure.

The Mexican GSM carrier with a prepay plan is Telcel, who is promoting
their "Amigo" service on their new and expanding GSM network. I was
surprised to see the Spanish carrier MoviStar on the air as well, but
don't know if they had a prepay option.

Telcel's GSM network is new ... kinda like the state that Omnipoint and
Voicestream were in way back. They are basically limited to large cities
and towns. There was no problem in Cancun, but on the road to Xel-Ha, for
instance, coverage came and went. Playa de Carmen was an active spot,
followed by huge gaps, followed by very marginal coverage in Tulum and
Xel-Ha. when we went to Chichen-Itza there was no coverage, period.

What's frustrating is the fact that the road is littered with Telcel
signs pronouncing that you are in a coverage area, when there is no
GSM signal. This is because they are referring to their older, more
complete TDMA network to which you do not have access on Amigo prepay.

I was first concerned that the literature gave a 30-day lifespan for the
start-up minutes, as my SIM had been registered and assigned a phone
number in excess of 30 days prior to landing. I was told I "might" find
the initial 300 pesos to be "dormant" only to be revived upon adding the
first recharge. As it turned out, my fears were unfounded as the SIM was
considered "activated" at the moment the phone registered on a Telcel
tower ... not the moment it was assigned a number. But there were more
surprises...

Another unexpected downside was the cost. I was looking to avoid $1 per
minute international roaming charges by going local, but ended up paying
more. Telcel's tariffs are based upon the area code where the prepaid SIM
is sold ... in this case, Mexico City. One you are out of that zone,
calling anywhere else in Mexico is long-distance (about 60 cents per
minute). Even if you are calling another Amigo phone bearing the same area
code, you pay long distance if you are not both calling within the area in
which the SIM was sold and registered. International calls (including calling
a US cellphone that is roaming in Mexico) costs about $1.25 per minute! As
you can see, the charges can add up very fast.

Needless to say, buying some recharge vouchers ("fichas Amigo") was first
priority. They're pretty easy to find, but I ran into unexpected
difficulty adding money to my line. The first few times I tried, the
recharge PIN was rejected, but finally entered and stalled with a message
"The Amigo system is currently unavailable ... please try again later" ..
for hours on end. On one occasion the PIN was rejected 3 times in a row,
whereupon all attempts to add value resulted in a recording which said
"That feature is not available for your number". So I dialed *264 for
help.

After a few minutes on hold, I got to speak with an English-speaking
Telcel representative who told me that 3 unsuccessful attempts invokes a
fraud protection feature which prevents adding value for 24 hours. He did
say that my previous recharge attempt was "in the queue" and should be
added by 1:30 the next morning ... it wasn't. And by the next morning I
was still locked out of recharge attempts.

I finally figured out that the PIN rejections were probably related to my
phone's microphone inserting too much ambient noise into the audio,
because when I tried again after exactly 24 hours, I covered the
microphone and the same PIN was immediately accepted and credited. Oddly,
my 300 peso voucher resulted in 500 pesos being added to my credit. Weird.

Or perhaps not ... because as I made calls and checked the remaining
balance, the total seemed to fall a bit faster. I was wondering whether
the 500 pesos was really 500, or it was just an accounting convenience
that allows equalization of different per-minute rates from different
coverage areas. (T-mobile does this in the US. Easyspeak equalizes all
totals to a phantom rate of 50 cents per minute for the whole bucket).

The Telcel rep told me something else about recharges that I hadn't
realized. The cards bear a zone number reflecting the intended market. If
you buy one in Zone 8 of the country, you can only apply it while you are
in Zone 8. If you keep it in your wallet and travel elsewhere in Mexico
for later use, you may be in for an unpleasant surprise.

Would I do it again the same way? Probably not. But it was a valuable
learning experience.