I found an interesting page:
http://www.llv.li/amtsstellen/llv-ak-nummerierung.htm
From the formal point of view the entire +423 663 is not considered as shared revenue/premium rate numbering range.
But what about that e.g. :
http://www.new7wonders.com/index.php?id=400
The number they use for voting i.e. +423 663 90 02 99 belongs to: Mobilkom LIE AG +423 663'900?000 - 663'999?999 is "Mobile network number allocation for international Services" just like UM range
(
http://www.llv.li/pdf-llv-ak-mobile_...0032006_en.pdf)
But this 900 inside... :unsure: