Not necessarily, I have an old IBM that has a voice modem (the computer is about 5 years old, and its modem is of better quality then my new computer..but I have a cable connection so it doesn't really matter)..and it has a program called "Ringcentral" that can dial out using my regular phone line. I can set my recording to "Wave Mix" and feed the soundboard sounds directly into the phone line. Using the "speakers up close to speakerphone" method was just too low quality and the victim ended hanging up because they "couldn't hear me."
Yeah I just kinda babbled as I typed all that so if it doesn't make sense sorry
BTW, that program I have cannot be downloaded, as the company who owns it has moved to VoIP services (voice-over-ip or 'internet phone")..so you won't find it. Try a program called advanced call center (can be downloaded, but only used for 30 days trial)