bobrk wrote:virtualmike wrote:Cell phones have a "Send" key that tells the switch that the complete number has been dialed.
Right, but how does it know that the number is correct?
Much the same way a landline phone switch figures out that a number is correct. When it has received the number, it uses various lookups and tables to determine how to route the call. If those lookups/tables fail, then it gives the "call cannot be completed as dialed" error.
The difference is that with a landline phone, there's no indicator of "I've finished dialing--connect the call now," so various regulatory bodies have established rules, namely that a number must have a fixed number of digits.
Within CA, the CPUC further refined the rules so that a call without an area code must be dialed with seven digits (with the exception of the x11 numbers) and a call to another area code must be 1 + area code + seven digits (and the latter is permissible for a call in the same area code).
If one doesn't dial the correct number of digits on a landline phone, after a certain timeout period, the caller will also get the "call cannot be completed as dialed" error.
The rules about number of digits to dial do not apply to cell phones, because they have a "Send" key.
If you think that's confusing, try many international destinations, where the number of digits to dial can vary, depending on the size of the town and its proximity to larger cities.