Following FCC pressure to end bill shock, cellular carriers now alert customers when they exceed usage allowances. We estimate a model of plan choice, usage, and learning using a 2002–2004 panel of cellular bills. Accounting for firm price adjustment, we predict that implementing alerts in 2002–2004 would have lowered average annual consumer welfare by $33. We show that consumers are inattentive to past usage, meaning that bill-shock alerts are informative. Additionally, our estimates imply that consumers are overconfident, underestimating the variance of future calling. Overconfidence costs consumers $76 annually at 2002–2004 prices. Absent overconfidence, alerts would have little to no effect.