Activate iPhone with someone else's SIM?

Hello! I just bought an unlocked iPhone 5 in the US, but I live in Germany. I don't currently have a working SIM card, and won't have one until I return to Germany in a week. However, I want to play around on the iPhone, put some of my music on it, etc. But I can't activate the iPhone without a SIM card.

My question is this: if I use someone else's SIM to activate my phone, will this cause trouble when I bring the phone to Germany? Or can I simply put in a German SIM when I get back and have no troubles? And secondly, will it cause any trouble with the friend's phone??

thanks