Hello Allyson,
I am not Sky subscriber but your question is down to basic Contract Law
When you took up your Sky subscription you signed a contact and agreed to be bound by the terms therin. Part of that contract will probably have allowed Sky to amend or change the terms of the contact, subject to them giving you notice of changes in by some specified method. It may be via notices in national papers, but most usually such changes are notified by post.
If you original contract required a permanent phone line connection, and sky have not advised you differently, then you are still bound by the original contract and should maintain a permanent phone line connection.
Contacts issued after your own may have had that clause modified, but that has no bearing on your own contractual obligations.
If you are in doubt about your current contract, you can only contact Sky for advice.