Teams Phone - Dial by extesnsion

Hey all, 

We are looking at using extensions as a means for users to call an auto attendant number (toll-free) and then allow users to connect to a specific user by dialing their completely phone number. My understanding is this extension can be assigned to one or either of the following AD / Azure AD attributes:

TelephoneNumber

HomePhone

Mobile

OtherTelephone

My question is, is there a limit to the how many numbers can be used in an extension?