Formula companies can obtain new mothers' addresses a number of ways:

They sponsor early pregnancy information sessions and offer "free
gifts" (without saying what the "gift" will be) for attending
couples.  While they can't get names from hospital staff, they may
approach the company that takes the baby photos, or any other
agencies which are given access to the hospitals.  They then send a
letter offering a gift package (again, not mentioning what the gift
is), which the mum has to mail a form in order to receive.  That way,
since she has "asked" for the gift, they can say the cans of formula
are "unsolicited".

Jennifer Landels, BA, CE
Vancouver BC