Nikos,
There are several options available to you. Take a look at this link for the options:
http://www.cisco.com/en/US/products/ps10536/products_relevant_interfaces_and_modules.html#voicemod
This module is a good candidate based on your high level description:
VWIC2-1MFT-T1/E1 | √ | √ | √ | 1-port T1/E1 Voice / WAN w/ Drop & Inser |
In addition to the T1 module, you will need DSPs. DSPs are used by the router for voice termination, media mixing, transcoding, etc. DSPs for the ISR (and ISR G2) are provide on carrier cards called PVDMs. Your router support the PVDM3 (generation 3). Review this sheet to help you pick the PVDM that is right for you:
http://www.cisco.com/en/US/partner/prod/collateral/modules/ps3115/data_sheet_c78-553971_ps10537_Products_Data_Sheet.html
HTH.
Regards,
Bill
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