Hi Amir,
The 3845 does supprt 240 IP Phones by default. Here is a way to check;
The max-ephones command limits the number of Cisco IP phones supported on the router. The maximum number you can set is platform- and version-dependent. Use CLI help to determine the maximum number of ephones you can set, as shown in this example:
Router(config-telephony)# max-ephones ?
<1-240> Maximum phones to support
Hope this helps!
Rob