serious problem

Hello IRVING18,

Thanks for using Apple Support Communities.

Since other people are having issues hearing you when calling, please follow the steps from the article below to resolve the issue:

1. Make sure nothing is plugged in to the jack connector.
2. Make sure nothing is blocking any of the microphones (refer to the pictures below to find your device's microphones). Check for these:
• Dirt or debris
• A screen protector or case
• When you're holding your phone next to your ear, make sure you don't block the microphone with your fingers or shoulder and make sure to speak into the microphone
3. Turn the iPhone off and then on.
4. Update to the latest version of iOS.
5. If necessary, find general iPhone hardware troubleshooting suggestions.
6. For further assistance, contact Apple Support.

iPhone: Microphone issues

http://support.apple.com/kb/ts5183

Take care,

Alex H.