Problems with IPhone 4s

Hi,

I purchased my Black 16gb iPhone 4s about 2 weeks ago, with a 2 year apple protection plan.

Yesterday I accidentally dropped my iPhone on the driveway and the screen cracked.

This morning I took it to the local tobacconist (whom also fixes iPhone screens), and got the screen replaced.

I picked it up this afternoon and was told he didn't have and black fronts, so he replaced my broken screen with a new white one, and replaced the back so it matched. Will this void my warranty???

A little bit later a friend borrowed my iPhone to ring her boyfriend and she couldnt hear anything through the ear speaker (top of iPhone near camera). I did a few practice calls to voicemail and it still didn't work, yet it worked before I got my screen fixed....

I've tried plugging my headphones in and taking them back out again several times, but nothing's changed. Also tried restoring my iPhone to factory settings but that didn't work either.

Any ideas as to what's wrong/how to fix it?

Did something go wrong when my screen was replaced or is it a fault with the iPhone itself?

Any help would be much appreciated.

Thank you.