The problem you are experiencing is not tied to a specific Express Modem hardware. It depends on what country settings you are currently using with your Express Modem software. On a PowerBook 200 Series (Duo) the country settings are controlled by an external DAA country code. On a PowerBook 500 Series with Express Modem II the System software country code controls the settings.
There are countries like France and Spain where PTT protocols do not allow blind dialing. Hence, the atx3 command or EM CDEV checkbox have no effect in these countries. If you are using Express Modem v1.5.4, only the ';d' "hack" works to enable blind dialing in this situation.
In next release of the Express Modem software (v2.0) the checkbox will not be displayed when you are in a country where the feature is not allowed.
Workaround
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Put ;d in the Dial Prefix box or as the first two characters of the phone number (for example, ;d5551212). This will force the modem to blind dial.
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