If you travel a lot and/or live outside of the US and require the appearance of being in the US, then Google Voice is for you.
Google voice is a VoIP service which works very similar to normal VoIP services plus you get a pretty reliable texting service too.
You can find more information on Google voice here. Below is a diagram to explain how the system works and how you can use to appear as if you are calling from a US number even while traveling.
The integration of the Google Voice App is very good in Android phones. On iPhones not so. On iPhones, your integration will be more like when you are traveling, where you need to use both apps (the Google Hangouts Dialer and the Google Voice App for individual functions).
There are a bunch of really good articles on how to use Google Voice and the Google voice dialer out there, so I will not plagiarize them. Instead here are some useful links.