How many SIP-client does one asterisk server support?

I really would like to know how much SIP-client does one asterisk server support. I have known that asterisk is not a complete SIP server so how many client can I use with one of this? Or you can give me some reference.
Thanks. (If it possible to make only asterisk as SIP server.)

There is no real limit, just a function of hardware as best I know. Good to check out the wiki for hardware details:

And the book also has sizing details:

Asterisk - The Future of Telephony