Depends on your GPS and the object. mkgmap adds the address information to the POI. For phone number, you have to find something yourself. I add some of this informations I need to the name of the POI.
Yes, it is possible. I don’t have access to the details right now, but you should be able to find out how when you look at the output of IMGfromGPX. If you don’t close the dialog when IMGfromGPX is finished you can access the temporary files.