The customer management system. Preferably PHP

If you mean it management system customer relationship (CRM), then you may want to look at
Highrise (http://highrisehq.com). Developers 37signals, known for their Getting Real approach. Their philosophy is to create products that, on the one hand, extremely functional, and with another — as simple, convenient and fast. So simple that you can reduce there is simply nothing.
\rwww.crmmag.ru/2008/12/04/obzor-crm-sistemy-highrise/ — brief description of the system.
However, if there is a scheduler, I can not say.
We used another product from the same office — Basecamp (http://basecamphq.com). This is a project management system that provides the ability to assign new tasks and mark the finished, control points, correspondence with clients and developers the ability to upload files as well as time-tracking (which is true, yet still can't properly implement — proprietary Dizy and artists actively ignore).
Information about customers is stored there. Format company for which you are developing the project (addresses, telephone numbers, etc.), and employees who have access to the project (contacts, position, access rights). Any additional data can be stored inside the project, attaching as a file, or by creating the entry in the notebook. The system is available in several languages.
Perhaps you will be enough.
Well, minus system — a rental charge for use.

Perhaps "Megaplan"?

There is certainly www.simplecustomer.combut she's clinically simple, perhaps even primitive.

Try www.sugarcrm.com

Light
\r
\rcrm.zoho.com/crm/login.sas convenient
\rwww.qcrm.ru/index.php — Russian
\rfatfreecrm.com/ in ruby
\r
Cool, you can put on yourself
\r
\rwww.vtiger.com/
\rwww.sugarcrm.com/crm/ leader
\rwww.civicrm.org
\r
We stayed fatfreecrm.com/ she has her own ideology. We strongly ruled by regular transfers.

I free never found
\r
stopped at bantamlive.com in the end