As an OEM product from RTX Telecom the hardware design is largely fixed, but Aastra has a lot of control over the firmware. I know that snom has made considerable progress with firmware enhancements for the m3 since it was introduced to the US about a year ago.
Unlike the m3 the MBU-400 has a single FXO port on the DECT base radio that provides analog life-line capability. Several people I know have expressed interest in this systems as they have VoIP accounts but also maintain a traditional POTS line in their home or small business. The FXO port would seem to make the MBU-400 the preferred option in such situations.
However, today I noticed a post to the VoIP Wiki at www.voip0-info.org by bbarnett. He tells of problems with the MBU-400 and also of trouble dealing with Aastra to get the problems acknowledged or addressed. That’s certainly unfortunate as the device has considerable promise.
I don’t know this person, nor do I have any first hand experience with the MBU-400. If anyone can offer up additional experience using the device I’d be happy to hear it. I’d buy one myself and give it a thorough review, but I already own snom’s m3.