German MVNE Telogic (fomerly known as vistream), from whom SIM&WEB and Freetime Telecom obtain their German numbers as well as the German IMSI (which forms the basis for coverage in Germany), has declared insolvency as of July 25th. Customers of solomo, Telogic's prepaid brand, report failure of many services including reachability from other networks and failure of Internet access as well as outgoing calls (see Telogic in vorläufiger Insolvenz: vistream-Nachfolger abgeklemmt - teltarif.de News). Against this background I fear FTT customers are also affected and so will have no or limited service in Germany.

At the moment I can make only outgoing calls with the German number.

In the meantime German VoIP provider sipgate who had a service called "sipgate one" that consisted of a mobile number from Telogic that could be forwarded to any other German mobile or landline number as well as to a Skype account free of charge, recommend in their blog to immediately export these numbers to another mobile provider. This doesn't sound like there is a chance service to be ever restored.

I have a Sipgate DE DID (not FreeTime Tele). Am I in danger of losing it?

No, sipgate's normal VoIP service based on geographical DIDs is not affected. It's just "sipgate one", a service that was only available to invited users as part of their beta test and was based on mobile numbers from the insolvent MVNO Telogic.

Sipgate offered its standard VOIP landline numbers to the US market under the name Sipgate One as well:

sipgate one