Mobile phone: boy or girl?

In Portuguese, the expression "thank you" is either "obrigado" (when said my a man) or "obrigada" (when said by a woman).

At the bottom of any supermarket recipt one can discover "obrigado" in masculine form, and this does not depend on the gender of a cashier, but rather indicates the neutral form, which just happens to be masculine historically.

Now, my mobile phone says "obrigada" when I credit it with some money. Why do they want to pull here by making it feminine?