So, you want to advertise 800-ESURANCE but it has 11 digits. A number over 10 digits is considered an over-spell number. It is a phone number that uses extra phantom digits to complete the spelling of a word. The call will be routed based on the first 10 digits whether they are omitted when dialing or not. An issue may arise with certain carriers when dialing these additional numbers. This issue is totally dependent on the carrier that you use.
An issue may arise with certain carriers when dialing these additional numbers. If a "1" is not dialed before the number then certain carriers like T-Mobile will not know if the number is international or not. The solution is to make sure that "1" is always advertised if your number uses an Over-Spell number.
Vanity numbers often use over-spells and carriers like Verizon have no problem when the missing "1" is not used.