How can I recieve incoming calls without the caller having to dial an extension?

You'll need to ask a more detailed question. Is this MVP, Contact Center? What is set up? etc... What kind of access do you have to the Business Unit in question?

You can arrange for a Direct Dial Number if you do not already have one is the simple answer.

Or on the other extreme. If it is in the Contact Center and you have a list of numbers that would be calling you specifically, you could create an integration that looks up the ANI of the inbound call and look up that number in your list/CRM/Database/etc. If a match is found route the call to you before it asks the caller for an extension. So the callers experience (if it is a known number) is that the number goes directly to you.

It just depends on specifics.