Mobile phone voicemail

Hi all,

I have just recently install Asterisknow and all was going well until somebody notice that sometimes when you dial a mobile number ( in Ireland prefix: 086 xxxxxx, 087 xxxxxx, 085 xxxxxx) and you connect to voicemail and your asked by the voice prompt to leave a message after the tone, you don’t get the tone, just silence and you end up disconnecting without a message being left, has anyone come across this issue, if so is it an issue with Asterisk timing or a combination of Asterisk timing out and that person voice mail not giving a enough time to complete the call?

Regards and thanks for your help:)