Let the hive mind of Engadget get that for you.
"I'm in the market for a new phone and money isn't a limitation. I'm also not partial to any particular US carrier, but here are some of the features I'd like to have: WiFi, GPS, good coverage in lots of places, push Gmail (a must!), physical keyboard (a must!), a touchscreen, decent battery life and a relatively slim body. And please, nothing that has a fruit logo on it. No offense to the fruit fans, though. Thanks!"
MTM, it sounds more fluent as it is more widely used, hence you are (we all are) more familiar with that sentence structure. However, the correct one is the one you mentioned (Imagine a mirror with which you can make calls) or morphing the sentence to something like "Imagine a mirror you can also use to make calls". The problem the Samsung's approach becomes more apparent when you add more things to what you can do with the mirror (Imagine a mirror you can also use to make calls, text your friends, browse the Internet while playing PacMan with). You get the gist.