No, your PSTN line, whether it is with us, BT or someone else, will remain unchanged.
==How can I improve resilience?==
We offer 3G fallback, where by you have a SIM, and possibly a dongle and other hardware from us, then the 3G SIM will be used for fallback. Contact Sales for more information.
We can also provide multiple lines, and these can be a mix of TalkTalk Wholesale and BT Wholesale for greater separation.