Currently, for agents to log in and out of queues, we tell them to dial *52 and press 1 or 2 at the IVR prompt. However, it would be easier if they could dial a shortcode which toggles the current status (in/out) and also can be monitored by BLF.
Welcome @PhonePhoenix to the forum.
In fact: everything you are asking for is already available.
Goto PBX/Tools/Asterisk CLI
Type core show hints
and send it.
It will show you for example:
QAL_18_1000
18 is the extensionnumber and 1000 is the Queuenumber.
You can use the QAL_18_1000 as value for a BLF-key as well. It will then light up accordingly.
Pause/Unpause would be:
QAP_18_1000
KR
Thank you for this 
I had a look at core show hints but can’t be certain, does this also exist if no queue number is specified? The idea is to log in and out of all queues at the same time.
This feature is not available afaik. You could write your own dialplan for that.
Queue Numbers must be specified.