It might be possible, and I did start down that road, but the query got pretty scary. I think I'm more comfortable with multiple queries, but maybe I'm wrong. Here are all the queries, the first generates the client list, the rest populate the integer fields:
SELECT c2.id, c2.name as 'client'
FROM client c2
WHERE level = 50 and status = 1;
SELECT c2.id, c2.name as 'client', count(*) as 'ext'
FROM client c1, client c2
WHERE c1.level=100 AND c1.status=1 AND ext.type = "phone"
AND c1.parent_client_id = c2.id
GROUP BY c1.parent_client_id ORDER BY c2.name;
SELECT c2,id, c2.name as 'client', count(*) as 'vm'
FROM extension ext, client c1, client c2, extension_prefs exp
WHERE ext.client_id = c1.id AND c1.level=100
AND exp.param="voicemail"
AND exp.value=1 AND c1.parent_client_id = c2.id
AND exp.extension_id = ext.id
GROUP BY c2.name;
SELECT c2.id, c2.name as 'client', count(*) as 'ivr'
FROM extension ext, client c1, client c2
WHERE ext.client_id = c1.id AND ext.type = 'ivr'
AND c1.status = 1 AND c1.parent_client_id = c2.id
GROUP BY c2.name;
SELECT c2.id, c2.name as 'client', count(*) as 'queues'
FROM extension ext, client c1, client c2
WHERE ext.client_id = c1.id AND ext.type = 'queue'
AND c1.status = 1 AND c1.parent_client_id = c2.id
GROUP BY c2.name;
SELECT c2.id, c2.name as 'client', sum(if(value<11,1,0)) AS "conf10"
FROM extension ext, client c1, client c2, extension_prefs exp
WHERE ext.client_id = c1.id AND exp.param="conf_size"
AND ext.type="conference"
AND c1.parent_client_id = c2.id AND exp.extension_id = ext.id
GROUP BY c2.name;
SELECT c2.id, c2.name as 'client',
sum(if(value<20 AND value>10,1,0)) AS "conf20"
FROM extension ext, client c1, client c2, extension_prefs exp
WHERE ext.client_id = c1.id AND exp.param="conf_size"
AND ext.type="conference"
AND c1.parent_client_id = c2.id AND exp.extension_id = ext.id
GROUP BY c2.name;
SELECT c2.id, c2.name as 'client', sum(if(value>20,1,0)) AS "conf30"
FROM extension ext, client c1, client c2, extension_prefs exp
WHERE ext.client_id = c1.id AND exp.param="conf_size"
AND ext.type="conference"
AND c1.parent_client_id = c2.id AND exp.extension_id = ext.id
GROUP BY c2.name;