For a workaround, use H.323 instead of MGCP if a fractional PRI is necessary.
As an alternative, busy-out the B-Channels that you are not using in Cisco CallManager by performing these steps:
Note: This procedure is not TAC-supported.
Open Service Parameters by choosing Services > Service Parameter. Choose a server and Cisco CallManager service on the Cisco CallManager Admin page.
The device name must exactly match the gateway name on the top of the gateway configuration web page. For example, S0/DS1-0@SDA123456789ABC = 0000 1111 0000 0000 0000 0001 (24 bits for T1. Channel number begins with 1 to 24 from left to right. The last one specifies the D-Channel, which is not affected. In this example, 5th-8th B-Channels are out of service).
Copy and paste that field into this service parameter to avoid any manual inputting mistake. = is mandatory and unique to distinguish the Device Name and B-Channel Maintenance Status fields. B-Channel Maintenance Status = xxxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx, where x can be one of these:
Graceful out of service. Change channel status until the active call ends if an active call exists on that channel.
Forceful out of service. Tear down the active call first. Then, change channel status immediately if an active call exists on that channel.
The system treats any other value as invalid, and the value does not take effect. Make sure that the total number of x is either 24 for T1 or 32 for E1. Any other invalid length or mismatch (24 for E1) gets treated as an error, and no action gets taken for that device.
Make sure to check Enable Status Poll on the GW configuration page through Cisco CallManager Admin.