Roaming

While roaming, the phone attaches to a partner operator's network, most often outside the borders. The home operator, for its part, continues to carry the subscriber's billing and identity.

An SMS bound for a French number follows the same path, whether its holder is in France or elsewhere: it's the visited network that handles the final delivery. Only reception can arrive with a delay when the mobile drops out of coverage; sending, for its part, asks nothing more of the sender.