New slot-allocation schemes are studied for the introduction of multi-rate services into digital mobile communication systems. In order to increase the traffic carried in such multi-rate service systems, channels have to be allocated dynamically to any rate. Rut with dynamic allocation schemes, narrow-bandwidth calls are frequently reassigned to new channels in the same cell, in order to clear the channels requested by arriving wide-bandwidth calls. Such call reassignments decrease the transmission quality, especially for data. We study new dynamic allocation scheme variants for minimizing this effect. The proposed allocation schemes are evaluated for the PHS (Personal Handy-Phone System), the Japanese standard for digital micro-cellular communication, but derived results should be valid for other cellular communication systems (GSM, DECT, ...).