VVX 1500 standalone installation - questions

Hello, i have installed the phone standalone behind a Fritzbox 7590.
It works, but there are some questions.

I can reach the phone with the browser, but the option "skype for business" is greyed out.
I think, i wouldn´t use this, but can i use the camera and mic with normal skype or whatsapp ?

I can dial landlines or handy numbers, but dialing a hotline with a servicenumber 01805 is rejected.
I haven´t found a filter for this.

If the display is off after 10 minutes the led up right starts blinking. Why ?

I was not impressed about the sound quality. I thought, with the big speaker and the dsp mic it would sound better. All parameters around hands free are default. 
Is there a better parameter set ?

The firmware is 5.7.4.1087. Should i update to newer fw ?

Thank you for your time.
Kai