I have ported my 027 telecom number across to a Vodafone mobile and all was going well until testing the voicemail. 

When the phone is switched off and someone rings its number from a telecom phone (landline or mobile) they recieve the disconnected number tone rather than my voicemail message. 

If you ring my mobile using another phone on the vodafone network it correctly goes to voicemail.

Interestly when the phone is on and someone rings it from a telecom phone and I don't answer the caller does get the voicemail message and they can leave a message.

On the fourth call to the Vodafone call center I was finally told that it "might" be one of the teething problems being experienced with the number porting and the techs were working on it.  No indication of a likely resolution time though.