Several scenarios require a phone to operate without first dialing a 9 to get secondary dial tone. The method to accomplish this seems to change from version to version as features migrate.
If accessing a single trunk for every call placing a line appearance may be an option. Since this is very limited in practice (must be analog CO line and a 1600 phone) it’s not practical.
User Short codes
Using a user shortcode is most practical and consistent. In R5 we tested several methods based on older results and found that the code xN would match correctly and return the desired results. The code would match any number followed by any string of numbers. The result N is then sent to ARS to be filtered and routed based on dialing rules. Since we matched any number, the preceding 9 is not required in order to access ARS. The call still follows standard rules on call barring, trunk and route selection.