Believe the DSL-2640R is a standard Dlink (unlocked) router, tho' it may have an ISP custom user ID & pwd to get into it, but that can be removed by resetting router to factory. It's the DSL-2640S that is locked, to Sky.
You can look out for Netgear DG834GT, DG834G v4 or the Netgear/Sky DG834GT or DG934G; the latter 2 are locked to Sky but may be flashed and unlocked.
1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 19 Meg WBC