The first and most important component of a good telephone call is always the phone itself. Businesses generally have a PBX system or some higher quality telephones, and the richness of the audio in the conference reflects this. Purchase an inexpensive phone, and the call will reflect it.
Recently, headsets have become very popular in the business world. In prior years, only customer service and call-center agents made use of them. The last few years have seen a rise in the number of businesses that have begun outfitting their employees with headsets. We recommend any headset from Plantronics (http://www.plantronics.com). These headsets are generally more expensive, but with features such as noise cancellation and secure communications, they provide superior quality as well as comfort for the wearer. Their top of the line models even work wirelessly with any desk phone. Beware of lower priced and lower quality headsets. They can damage a conference call faster than any other factor.
Speakerphones are generally considered poor for hosting conference calls. Some of the top of the line speakerphones, such as the ones from Polycom (http://www.polycom.com) are better than most, but because of the sensitivity of the speaker and the close proximity of the microphone, they have a tendency to introduce extra noise and sometimes echo into the conference. If the phone is on a conference table, then if someone bumps the table accidentally with their knee, the sound vibrates the entire table, and by default, the speakerphone itself. The entire conference must suffer through these little clicks and bumps. This is why speakerphone use is generally discouraged for a conference.