Ringer acting weird and videos won't play

[LindelJones27]

My daughter got an iPhone 5 earlier this month.  At first, the sounds were acting strange (phone would vibrate but not ring during calls, texts, etc., although talking on the phone worked)  and sounds would sometimes work and sometimes not.  Videos would also not play at all (although it is not a user error as the has an iPad 3 that works the same way.)  At first we thought the external speaker was broken or on its way to breaking, but when I called her and she tried putting it on speaker, all sound began working--ringers, phone calls, everything.  Even videos will work now.  Don't know what is going on........?  And if it breaks permantently, can we get it fixed free of charge?  Thanks.

--Lindel