The Patriot Act allows us, the government, to grab "tangible things."
This includes things that you may not consider so tangible, like electronic records.
We, the government, can use these records so long as it's relevant to an investigation. There's a complex legal definition, but we looked it up in the dictionary for your sake.
Technology produces tons of data. Sadly, technology isn't so advanced as to be able to read our minds and find exactly what we're looking for. So bulk gathering it is!
But don't take our word for it. Congress probably meant us to adopt an expansive view (quiet, Rep. Sensenbrenner).
But we know our limits. We promise not to go after your medical records, if only because they'd be useless to us.
By the way, the Fourth Amendment doesn't apply here. But let's suppose it did.
Since it'd be exhausting for us and a lot of wasted tax dollars for you, it should be okay if we got permission from the FISC in advance to seize future phone records.
And it's all constitutional. So we're good, right?