Hi,it is possible with some modules like
EVM-HD-8FXS
http://flylib.com/books/en/2.10.1.64/1/
Eight ports on the baseboard that can be FXS or DID. You can expand the EVM-HD to up to 24 FXS ports by adding two EM-HDA-8FXS cards, or up to 12 FXO ports by adding two EM-HDA-6FXO cards, or various combinations of FXS and FXO by adding one or two EM-HDA-3FXS/4FXO cards. The EVM-HD supports any combination of two EM cards.
Hope it helps...