Let's make sure we're in the right place by checking the routing. If you have loop start lines go to SYSTEM/DEVICES.../CO TRUNK GROUPS and find your main group. Look at DAY RING IN TYPE, should say SINGLE and the destination field is where the calls go, hopefully that announcement you mentioned. If you have T!/PRI or SIP, go to SYSTEM/TRUNK RELATED INFO/CALL ROUTING TABLES, find the table you're using and check ring in type and destination. In either case, for a sanity check, change the destination to a real phone, make a test call, see if the phone rings...then change it back.
Next now that you're sure of the application number open the app, open DIGIT TRANSLATION, change the destination to a real phone and try a call. If that works something is weird with your general mailbox...create a shiny new one, point timeout to it, see what happens.
Note: if you're running scheduling (STAR APPLICATION) your trunks will point to that first, then the regular business hours entry there will point to the auto attendant.