How long does it take for the iphone 4 to be activated?

I just upgraded to to the sprint iphone 4 and i went through the whole activation process and i'm able to call people but when i text someone, it has a red exclamation point and says "message sending failure". How long does the whole activation process take?

Added (1). The cellular data is on. I'm getting texts from people but it won't send

2 mins.
turn on cellular data in settings.