I found the following recommended steps for when the person you're talking to claims that you sound muffled or not loud enough:
- Check the volume setting on your iPhone. You can adjust the volume by pressing the volume up and down buttons on the left side of the iPhone.
- If you are using a third-party iPhone case, make sure it is not covering the speaker, microphone, or top microphone. Try making some calls without the case to see if a caller can now hear you more clearly or play music to see if the speaker's volume is better.
- If you have not removed the plastic display film used for protection during shipment, either ensure that the microphone and speaker are not covered or remove the film completely.
- Check that the speaker, microphone mesh covers, and top microphone hole are not clogged with lint or other debris.
- If the speaker, microphone mesh, or top microphone (iPhone 4 only) appear clogged, please use a clean, small, dry, soft-bristled brush to clean them. To do this follow these instructions:
- Use the brush to carefully and gently brush the speaker and microphone mesh.
- Brush away from the 30-pin dock connector to avoid getting any debris into the dock connector.
If the issue persists, go to: apple.com/support/iphone/service/faq/ for information on service.
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All the best,