911 Operator here, most cities won't follow up a 911 hangup call from a cellphone unless there is reason to think there is an emergency. In large cities, you get hundreds of accidental 911 calls a day and finding all of the phones (even if they are WPH2) would take more than the entire police department only looking for 911 hangup calls. In many cities, a 911 call from a land line will automatically dispatch PD to the address.

Following the advice above is very dangerous.