Anyone familiar with the SBC product lingo?

Hi All, I'm trying to get some pricing on an OC-3 that we will be using for voice. We already have a master agreement with SBC for our services. I have the feeling that we are being "oversold" services and/or sold services that are not required for what we need to accomplish. Not doing this everyday, I'm confused about the "Feature Name" of things like: SONET Circuit Service OC3-c (155Mbps) $2200 vs. Central Office Node Circuit Service OC3/3c (155Mbps) $675 Anyone that is knowledgeable about SBC lingo, please feel free to ping me. If you have experience with OC3s even better! ;) Thanks! Dan