Due to the 2015 spectrum auctions held by the German regulatory authority, the former DECT guard band has now been auctioned to Vodafone.
So contrary to before, all GSM ARFCNs in the E-GSM-900 and DCS1800 bands are now licensed to commercial operators.
As a result, obtaining an experimental spectrum license is now only possible within the band allocated to a commercial mobile operator, and with explicit permission of that operator.
Given that this happens only rarely and that the operators have nothing to gain by supporting Osmocom/OpenBSC and/or the CCC, the chances for this are very low.
As such, it is unlikely there will be any GSM network at 32C3.
If you happen to know sympathetic people in the radio network planning of a mobile operator, please contact LaForge by e-mail.