If a federal judge orders an injunction that shuts down BlackBerry email service in the United States, business customers have the option to switch to another wireless email platform. But migrating to another platform won’t come cheap, according to two consultancies that have analyzed the costs of such a move. Switching from BlackBerry devices and servers to a competitive platform will cost as much as $844 per client, according to a report to be issued on March 1 by the telecom consulting firm Telwares Communications.