Do phone numbers have negative numbers?

Answer 1

No.

Phone numbers are a collection of groups of digits which (originally) allowed easy routing of the call across the network. In the original Strowger automatic exchange (possibly invented as he felt that the local manual operator was not giving his undertaking business the calls it should) the switching relays had 10 positions, 1 corresponding to the 10 digits (1-9, 0) on the telephone dial. As the dial pulsed the line (0 pulsed 10 times) for each digit, pulses would be used to set mechanical devices in one of 10 positions; eventually, the effect of the settings would link the caller with the callee.

These days, the switching is done electronically, but the same coding system set up then is (mostly) used.

UK Phone numbers have two or three parts. The last part is the number of the subscriber at the local exchange; the part prior to this gives the local exchange number; if there are three parts, the first part is used to group local exchanges together. Originally when dialling a number on the local exchange only the subscriber would be needed; examples:

(020) 8123 4567

020 says London

8123 would be an exchange in outer London (as it starts with an 8)

4567 would be a subscriber attached to that exchange.

When dialling another 020 number, only the last 8 digits need be dialled.

(012345) 678911

012345 would be an exchange somewhere (possibly a small town or group of villages)

678911 would be a subscriber number.

Any number starting 07... is a mobile phone.

American (including US and Canada) phone numbers (as far as I know) are similarly split for a ten digit number:

123 456 7890

123 is the large region code

456 is a smaller sub region (akin to an exchange)

7890 is the subscriber number

When dialling in the same large region, only the last 7 digits need be dialled. There is a reserved sub-region of 555 which is not routed anywhere (and so not allocated to any subscribers) and is used for phone numbers in TV programmes (to avoid random members of the public getting calls from people who spot the numbers and try them).

As modern exchanges are digital, it is possible to think of the phone number as stored in memory as a number and not a string; as such, the bit pattern could either be interpreted as unsigned or signed. If interpreted as signed, it could be possible to think of a phone number as negative: for example with 16 bits, the possible ranges are 0 to 65535 (unsigned) or -32768 to 32767; if a 4 digit number is stored, it would be seen as 0 to 9999 in the positive range, but with sloppy programming it could be possible to think of 0 as -65536, 1 as -65535, ..., 9999 as -55537 (even though these numbers are out of the normal range or signed 16 bit numbers, they are the last 16 bits of a 32 bit signed value of those negative values).