When is M$ Access ok?

For some simple-minded reason the ridiculously expensive auto-dialer software I’ve seen uses Microsoft Access databases. I haven’t worked a whole lot with very large databases but it seems to me that if you had two T1’s (48 lines) dialing simultaneously from a persons database of roughly five million checking each number against the national do not call list, another easy five million if your selective with the area codes you load, you would use something other than Microsoft Access. Due to the hardware requirements of such computers the software vendors usually make you buy pre-configured setups w/the software installed. That’d make it pretty easy to install/depend on a real database system.

What exactly is the ‘acceptable’ cut-off mark for using Access as your applications database? Can’t say I use Access but I’d like to know the answer regardless.