Hey there,
I would build the CRM using Ruby on Rails (though I could of course write it in PHP). That way, I would be spending my time testing the code rather than just writing it (PHP has a lot of "fluff").
Also, I would put the 'Transaction Tracker' on the Home Page, just so your agents would spend *their* time looking at the conversations with your customers, rather than navigating menus!
If you're interested, contact me and I'll break down the needed work into smaller modules, so as to give you an estimate of how long it will take (approx. 10 days).