You can play one single stream at a time on a single account. If you're streaming music from your iPhone, you can't stream music from your computer at the same time. If you're streaming music from your home audio system, you can't stream music from your iPhone or computer at the same time.
However, Rhapsody offers many playback options. You can stream from your phone while playing downloaded tracks from My Library on your computer, for example.
I have Rhapsody Premier Plus (Rhapsody To Go) which allows up to 3 devices. Why can’t I stream concurrently on 3 different devices?
Rhapsody Premier Plus (RTG) customers are allowed to transfer subscription music to up to 3 compatible devices. Although you can't stream music from more than one of your devices at once, you can stream from one device at a time while playing music offline with the other two.