Hello Belal,
Yes, the HWIC-4T serial interface should support X.25 (as the X.25 is primarily concerned with Layer2 and Layer3, a serial interface being a Layer1 component is actually relatively independent of the X.25). Your IOS feature set must be properly selected to also support the X.25.
Make sure to obtain the proper serial cable type - according to the interface type on your X.25 modem. X.21 or V.35 are among the most common.
Read the following documents for more information:
http://www.cisco.com/en/US/prod/collateral/modules/ps5949/ps6182/product_data_sheet0900aecd80274416.html
http://www.cisco.com/en/US/prod/collateral/modules/ps5949/ps6182/prod_qas0900aecd80274424.html
http://www.cisco.com/en/US/docs/ios/wan/configuration/guide/wan_cfg_x25_lapb_ps6441_TSD_Products_Configuration_Guide_Chapter.html
Best regards,
Peter
