It was made very clear to us that if we didn't hire a DJ, our planner would not be filling the role of MC. We used the iPod setup and had a family member switch between playlists/pause at the appropriate time. There was a microphone for the speeches, and our officiant (a family friend who stayed for the reception) made a blessing that announced brunch.
Since ours was just a small, casual brunch, we didn't feel the need to be announced or to tell everyone what was happening whenit was pretty obvious. When it was time to cut the cake, we just let the staff know, walked over to the cake table and kinda waved at everyone so DH could make a speech.
However, if you are envisioning a traditional receptionespecially one with general dancing, not just first danceswhere the couple and attendants are announced, the buffet is announced, the dances and speeches are announced, etc. you will either have to get a friend/family member who really knows what they're doing or hire a DJ.