Hmmm, as interrupting to answer at the time has the additional overhead of task/context switching, I'd say it's more. If you just switch to/from the voicemail

Hmmm, as interrupting to answer at the time has the additional overhead of task/context switching, I'd say it's more. If you just switch to/from the voicemail context once for 10 messages, the cost is only 10% of the cost for real-time answering.