This is a note to my self – and all the material is straight from this site: http://tomsalmon.eu/2012/08/mounting-samsung-galaxy-s3-using-mtp-on-debian/
You should totally check his blog out – there are a lot of good stuff there..
Now for the guide:
To mount the phone in Debian (Wheezy/Testing):
apt-get install mtp-tools mtpfs
plug in the phone
mtpfs -o allow_other /mnt/phone