Stop iPhone alerting me when I'm in a phone call
Solution 1:
Looks like there is no setting to silence alerts during a call.
https://discussions.apple.com/message/16904276#16904276
There's no phone setting to silence alerts during phone calls. You can suggest this to Apple: http://www.apple.com/feedback/iphone.html
Solution 2:
Set Settings > Sounds > Vibrate on Silent to OFF; then while on the call you can flip the hardware switch to Silent. This will disable all sounds and vibration.