Often I would switch my phone to silent mode (so that no one among my workmates, and especially my boss, realises that it's ringing) and intentionally not answer the incoming calls from French speaking customers, and then call them back in a suitable moment. There were two main reasons why I would do this: first, nobody at the office knew French. People tend to fear the opposite: that the others listen to what you're saying and judge it - so it may sound silly but I felt rather guilty and embarrassed that they couldn't understand a thing! The second reason seems less paranoid: I procrastinated in some way to feel "readier" for the call, plus wanted to be considered as someone who is always busy but, at the same time, who always calls back :D