Did you know you can put calls on hold on iPhone? This suspends the phone call without hanging it up, but it prevents you from being able to hear the individual on the other end and they can’t hear you either. It’s a slightly hidden feature that you won’t see at the normal phone options, but here’s how to use it:
While on a all, tap and hold on the “Mute” button until it turns to “Hold”
Tap it again to resume the call as usual
Apparently this is only available on GSM enabled iPhones (AT&T and T-Mobile in the USA), and the Verizon and Sprint iPhone doesn’t support the feature on their networks. Users on CDMA networks can always just use the Mute feature instead though.