But getting something like the Linksys ADSL+2 (ADSL2MUE)
http://www.amazon.co.uk/exec/obidos/ASIN/B0007SQG62 and plugging that in will do the same job as the Cisco must be wanting an ethernet RJ45 connection not a telco RJ11 connection.
However at £42 there are cheaper all in one boxes.