Generate a file with random contents, certain length, and fixed beginning and ending characters (phone number in file size).

number.sh

#!/bin/sh

if [ "$#" != 4 ]
then
	echo 'USAGE: number.sh ~/my-phone-number 12065555555 o o'
	exit 1
fi

echo -n "$3" > "$1"
base32 < /dev/urandom | tr A-Z0-9\\n a-za-z | tr -d '=' | head -c $["$2"-2] >> "$1"
echo -n "$4" >> "$1"