At the time both countries were at peace and neutral, although this was more theoretical in the case of France under the Vichy regime. I would welcome, in addition to a full answer, links and information describing the standard process for exchanging telegrams in each country in the general period (1930's - 1950's) as well as any special restrictions which may have been imposed due to the Emergency (Eire) or to appease Germany (France).
I have searched for Telegram, Ireland, Emergency, Vichy, Sending Telegram, &tc.
EDIT: While thanking those who responded for their time, I'd still welcome any specific knowledge or answers to this. I'm willing to accept this would be a difficult/costly undertaking at that but how could it work if the telegram was very important (to P&T as well as to the sender/recipient)? Remember I'm looking for how it would be sent and how it would be received, not the routing in between, lets stipulate it goes via the transatlantic cable to countries not (yet) involved in the conflict such as the USA and USSR.