Mommy fail = not realizing your toddler figured out how to unlock your cell phone and - amidst random button-pressing - managed to place a call.
Bigger mommy fail = not realizing your child is making said call and proceeding to leave a two-and-a-half minute voicemail that consists mostly of you in the background singing (poorly) to pop songs on the radio, interspersed with "don't put that in your mouth"s, and completed with "oh sh*t! Did you...what the...who are we calling?!?"
Saving grace = that the phone call was to your mother and not your ex-boyfriend who is just one more click down the contact list.
Note to self: I really should delete ex-boyfriends from my phone...