Reference: AT Commands Interface Guide for Open AT® Firmware v7.1
Revision: 008
Date: April 2008
The parameter description for +WRIM (on p161/193) refers to +CCELL (see bit 4).
What is +CCELL ? It isn’t defined or even mentioned anywhere else in the document! 
What happens if you AT+CCELL? alt. AT+CCELL=?
I haven’t had time to do any trials with 7.x yet myself, so I’m just curious…
They both give ERROR.
(Even with AT+CMEE=1 it’s still just ERROR).
The document just mentioned it as an “event” - so it may be just a response, and not a command?
AT+CCELL command is separately documented in “Cell Lock” application note.
You can find it in “Application notes” webpage.