If an incoming call arrives and it is unanswered and you then try to place an outgoing call, there is no dialtone - just dead air. You can still dial out but it is a little confusing not to hear dialtone.
The problem was reproduced with the latest magicJack dialer update that came out a few days ago on Windows XP, Vista and 7 computers.
The bug has been reported to magicJack customer service and they said the issue would be internally forwarded to the core technical support team for resolution.
Magicjack BUG - No Dialtone After Unanswered Incoming Call
Moderators: Bill Smith, Pilot