Yes it does use CG-NAT. IP address could/will/may (take your pick) potentially change every time a PDP context drops.

right i'm having some strange issues connecting to FritzBox remotely.. When on an external wifi connection in a different location i can connect using the MyFritz iOS app but as soon as i flick to mobile network i cannot connect to the fritz box... any ideas?

and just to add, the fritz box is on a bigpipe connection so my thoughts are that there is some blocking going on internally with Spark/bigpipe network. as wifi works fine in different locations?