EDIT: Didn't realize you were referring specifically to the sneaky pop-up. Agree with you on that one.
From a brief reading of it the other day, it seems data that is necessary to provide a contracted service (like, say, providing access to a cellular network) has a specific exemption to express consent.
Check out items 1a & 1b in Article 6 of Chapter 2[1]:
"1Processing shall be lawful only if and to the extent that at least one of the following applies:
A: the data subject has given consent to the processing of his or her personal data for one or more specific purposes;
B: processing is necessary for the performance of a contract to which the data subject is party or in order to take steps at the request of the data subject prior to entering into a contract;"