"Representatives from Verizon, Sprint and T-Mobile all declined to comment on Sunday in response to questions about whether their companies were aware of Hemisphere or participated in that program or similar ones."
If they were not participating in Hemisphere or similar programs, I'd expect them to be quick to say so.
If they were asked to comment on Sunday (on a weekend), then it's probably more likely that they wanted to confer with their legal departments before denying with any confidence.
This is especially in light of the recent public/media PR confusion with technology companies around PRISM.
"Representatives from Verizon, Sprint and T-Mobile all declined to comment on Sunday in response to questions about whether their companies were aware of Hemisphere or participated in that program or similar ones."
If they were not participating in Hemisphere or similar programs, I'd expect them to be quick to say so.