Yes, it's possible to couple a iNum or another DID number as your American number to your SIP address. I did do the same for my number. I can receive my calls now everywhere.
Making calls I didn't get work yet. I use Voipbuster.com for that. First I coupled my DID number to my SIP from Voipbuster, but that was a very bad idea. Because their app doesn't work on the background, and it was very unstable (at least for receiving calls).
I use Linphone for receiving calls, and it works great.
Could there be errors! Absolutely.
I use both Android and iOS. The problem on the iOS that I suffer still from is that it has stop running on the background. So I can't close the application. I don't know why, because it worked okay for some time. I didn't do anything strange. Just put it in flight mode when I go to sleep, next morning it didn't work anymore. A reinstall didn't help. I understood from previous postings that more people have problems with iOS 8.3 and Linphone running on the background if this solved than all would be okay. For now I have not accidently close the application, and than it works. I hope Linphone will solve this issue, because it's important.
For Android I run it on my Asus Fonepad first version. It nicely run on the background, although after some while it doesn't receive calls either. I guess it has something to do with the power saving modes. But that's not the worst problem, that is that it crashes when I take the phone after it rings. I haven't tried it on my Nexus 7.1 yet, it runs a newer Android "Lollypop".
But anyway I am planning to run on my iPhone anyway.
Maybe your question is "would it be wise to do so". I can say I'm glad that I did it. I'm now in a different country and can easily take my "home phone", even on 3G it works great.
But I must also say I'm quite new to it. I ported my number only a week ago.