Yep smarts extra 3Mb is just until the end of 2006.
Its unusual actually as they've previously only offered up to 6Mbps /512Kbps. Perhaps next year they'lll start taking full advantage of the ADSL2+ technology that they're using and offer the maximum 24Mbps /3.5Mbps
This is something most other DSL providers can't offer as they still use older tech like ADSL and RE-ADSL which offer up to 8Mbps/1Mbps and 5Mbps/512Kbps respectivly