A few things to know:

If you sign up as Smart Access you only have the choice of the $39 or $49
plans.

You must finish the entire year, and only then will they re-run credit if
you ask them to to see if you qualify for a regular account.

The $75 activation charge replaces the regular $35 charge, so it's not
really that bad (only really $40 extra).

Once you pay them the $75, you NEVER get it back, and unlike the $35 fee on
regular accounts, it is never refunded if you cancel during the 14 day trial
period.

Phones are usually cheaper at independent ghetto-looking mall shops, but but
on top of the $75 activation most stores charge extra for the phone on Smart
Access activations (lower commission paid).  Stores like Best Buy and direct
T-Mobile stores don't charge extra, so they might be better even though
their regular prices are higher.  DEFINITELY shop around and ask for their
smart access prices.

I've never seen a credit policy on paper, but it seems like Smart Access is
mostly given to people with little or no credit history (vs. having actual
"bad" information on your report).  One credit card for about a year is not
a whole lot of credit.  First, make sure you are talking about a real credit
card, not a debit card with a credit logo on it.  My guess would be that if
you do smart access now, another year of good credit card payments and you
will be OK for a regular account.  I used to sell them, and people 20 years
old would get approved for real accounts all the time.

For good credit in general, go to the Trans Union web page (or other credit
bureu, but TU is the main one T-Mobile uses) and pay the measley $8-10 to
get your actual report (or sign up for a free trial on an expensive service
and cancel it).  They'll tell you all the stuff you need to know about
credit directly, rather than trying to get the info from some idiot on
usenet or from the same silly news reporters that tell you the phone will
give you cancer and make your car blow up.