I suspect that @billg is referring to a different Wi-Fi network since there are no other cell network options for your phone. Trying Wi-Fi at multiple locations may help isolate the issue, so check several.
My guess is that low volume will not be a problem on cell calls but if it is then making sure the microphone aperture is clear is a great place to start.
Are you using the Equalizer? I haven’t heard of sound quality or volume issues with the E2 like there were with some of the E1 phones but you can check to see if it is turned off by going to the settings in the Play Music app:
- Tap the ‘hamburger’ menu in the upper right corner of the app.
- Tap ‘Settings’ and scroll down to the ‘PLAYBACK’ section.
- Select ‘Equalizer’ and make sure that it is turned off.
This may be a fishing expedition but it will give a more detailed picture of the way your phone is configured and may be nice to know in case you want to change the playback characteristics of music that you listen to.
Would a different phone help or a different sim?
Different phone maybe, but not guaranteed unless you determine that the issue is a hardware problem in your current handset. A different SIM will not affect the sound of your phone – on either end of the connection. The SIM gives you access to 4G data on the cell network for things like e-mail, web surfing, video or audio apps, etc.