This seems to be a bug of your Gigaset HX handset. Use a another phone. 

Analogue phones connected to the TAE port of your router in particular work much more reliably than the Gigaset HX handsets. 

It is not solution to use another phone. It is plain DECT handset. I cannot use analog phone. We are not living in 1990 to use analog phones with poor audio quality.

Everything is fine, but I cannot make outgoing roaming calls, or accept incoming roaming calls. It is so frustrating.

It’s not a plain DECT phone, it’s an CAT-iq 2.0 handset. And obviously it doesn't work correctly. o2 has no influence on the proper functioning of your own devices. If you cannot use an analogue telephone, the cause may also be your router. All routers issued by o2 support the connection of analogue telephones. 

By the way, there is no "roaming" in the fixed network, as it is a fixed connection and the o2 DSL contract can only be used on the contractually agreed DSL connection and nowhere else.

You mixed something up. It is ordinary IP phone. Every DECT station has support for CAT-iq dect, then it should support it. It supports it. Dont mix it. Everything works fine for any DE call, any mobile call, but any call made OUTSIDE Germany, is not possible. It has nothing to do with the handset! Same behavior is even with analog phone or softphone via SIP account. 

Statement that I cannot use analog phone is because I do not have place to put it anywhere near router to connect it to router. That is the reason why they even developed DECT phones and integrated DECT basistation in routers.

The Gigaset CL660HX is not an IP-Phone. Not every DECT base station supports CAT-iq 2.0, e.g. mine does not. What your router supports or not supports is not my business. 

If there is space for a router, there surely is also space for DECT base station. 

As you state that you cannot make calls outside Germany even with an analogue phone, it is likely that you have misconfigured your router. On the part of o2, dy default no international calls are blocked and in particular no incoming calls are blocked.

Who mentioned any Netgear router? What are you talking about? You know that CAT-iq is just one standard of many that handset supports. I told you already that everything works fine, except roaming calls, calls outside of Germany, however you want to interpret it. If there is support issue with protocols, then nothing would work.

Also, there are really not much options you can configure on O2 router, as most of the options are in their system and only they can change them. Like, auslandanrufsperre and similar blocks.

If you dont have a solution, dont blame my equipment as that same equipment worked fine before on another operator.

Unfortunately, you didn't talk about which router you use. Therefore I can only guess. 

In similar problems in the past, normal phones have worked normally while Gigaset HX handsets have malfunctioned. 

If you use a Homebox 6641/6441/6741 and the problem occurs when using an analogue telephone, I would recommend reporting this to customer service. 

Hello @hrvoje555, welcome to our o2 community :-)

The isue you are describing reminds me of a smiliar one with our o2 Homebox and a Gigaset 430HX. 

One was not able to accept the calls on the phone even if the calls reach the router and the phone. The phone was ringing, so the call was transfered and no barring or anything exists.

It seems like the Homebox and the Gigaset HX series do not really work really well together, either another compatible router or another phone would be a solution.

Regards,

Lars