Phone Issues

Why does everybody sound so different over the phone today? Well that's my biggest question for the day. In the morning I recieved a call from an unknown number. So naturally, I picked up the phone and said 'Hello' in the most dullest voice that I could ever muster. Then a female voice said 'Hi Senthil' The next thing I remembered saying was 'yeah?' I thought that Jillian was on the line. I was about to say Jillian? But fortunately I did not as it was Christina. She wanted to know the recording studio's number.
The next case happened later that evening. This time it involved Sara and Kylie. My phone started to ring and the caller ID showed that it was Sara. So I picked up and said 'Hey Sara, whats up?' And she answered back in a deep voice. She sounded different, but I did not ask or point that out. So naturally, I continued the conversation thinking that maybe she had a voice change or something. After the conversation was done, I put down the phone. Then, a few minutes later, the phone rang again. I picked it up. It was 'Sara' again. This time she asked me, 'Do you know who's speaking on the phone?' I said 'yeah I do. Sara rite?' 'Eh, this is Kylie lar. I was on the phone the last time around also....etc etc. There you speak to Sara.' And the first thing that Sara asked me was 'How on earth could you have mistaken Kylie for me?'
The last time I spoke to Kylie was when I was 17. I'm 19 now. Oh well..