Now that PN are in to the mobile market, it wouldn't be impossible for PN to send a data only dongle to their customers that have switched but are facing delays in either the order going through (new line for example) preventing the switch on or issues with actually getting the line connected (existing line but with a fault) or existing customers facing a long delay in getting back online (excluding major outages as it would cost way too much).
Some forum users report delays of over a week or so before they finally go live or get their fault fixed. PN would have a rough idea from OR as to when OR have a spare engineer etc etc etc.
At least it would allow certain devices to connect to the www at no (preferable) or low (to cover P&P) additional cost to their customers - examples: 1) a home customer whom may be working from home for the week and needs to send documents from his/her laptop and 2) a student needing to login to their school/college network.
Now I know that would depend on a mobile signal and would come at a cost to PN, surely these costs could be taken on the chin to keep their new or indeed existing customers happy.
I can picture the guy on the ads saying We'll do you proud, even if it means sending you one of our shiny new data only dongles until your fault is fixed or you go live!!