SELECT query with referenced subqueries
This works, there may be something more elegant:

 insert 
 select 1 as client, 'A' as [status], 500 as 'Size'
 into #temp
 insert into #temp
 select 1 as client, 'B' as [status], 1500 as 'Size'
  insert into #temp
 select 2 as client, 'A' as [status], 2000 as 'Size'
 insert into #temp
 select 2 as client, 'B' as [status], 800 as 'Size'

 select t.client, ta.size as 'A', tb.size as 'B'
 from #temp as t
 INNER JOIN (select client, sum(size) as size from #temp where status = 'A' group by client) as ta on t.client = ta.client
 INNER JOIN (select client, sum(size) as size from #temp where status = 'B' group by client) as tb on t.client = tb.client
 group by t.client, ta.size, tb.size