There should not be a problem being on the internet and using the phone at the same time. Unless you are experiencing problem with that, what exactly are you asking?
You are aware that the computer must be on and connected for the Magic Jack to work, right?
I have a Magic Jack internet phone device and would like to have it hooked to our home phone system all the time without going thru my laptop. Is there a device that will allow me to be online with phone and computer at the same time?