a weird message on my iphone 3gs?

[Mariam]

i was playing on my laptop when i heard a voice from my iphone, a message appeared on the screen "not a text message" and it said (( sorry you are not eligible for 1gb data bundle and wifi access next month as your usage is lower than the one required )). i don't have a monthly plan and i've been using the phone since 20.21.09 you can say around 9 months. please can anyone help and explain what is it about ?? thanks in advance