4S, microphone not working

my daughter has 4s iphone. when makes call or receives one, person on other end cannot hear her. can hear them however. siri, cannot hear her. puts on speaker phone, or facetime, works great. ideas, before take thing in service?
guys, , gals.

 

no on this? anyone? have not taken hers in service yet... but...
same thing happened iphone 4 today? bought on launch in 2010. bought 4s on launch 2011. latest software on both. tried restore on mine no help. anyone?

 

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