If you decide to setup your own callthrough service you can get a free Austrian DID from sipgate.at, who will assign a number from the 0720 or 0780 numbering ranges. Calls to these numbers are billed randomly - some Austrian operators bill them as fixed line calls, others like premium numbers. However a Vienna-based company has set up a gateway based on a regular fixed line number which allows calling sipgate.at numbers at fixed line tariffs.
Just replace the leading 0 by 01326:
072012345678 would become 013 26 72012345678
and
078012345678 would become 013 26 78012345678
Apart from an interruption that lasted a couple of weeks followed by a number change this gateway has been running reliably for more than 7 years now.
For more details see
österreichische 0720 Nummern zum Ortstarif (German)