As for a company providing information without a warrant, recent case law is closing/has closed the door on a company's ability to do such a thing (not that they are, considering how many companies have stringent privacy agreements with their users).
1. If a company (or an individual) provide information to law enforcement on request, without a warrant, is that disclosure itself breaking the law? (Ignoring company policy and privacy statements here.)
2. If so, will the company be prosecuted for doing so?
3. Will the information be usable in court?
When you say "recent case law is closing the door on a company's ability to do such a thing", it sounds like you're talking about #3 (but feel free to clarify if I'm wrong). But #1 is still a concern, because it can show the police where to try to do parallel construction.
Second, yes, law enforcement needs a warrant to legally compel a company to provide them with information. But what if the company (or an individual within it) is willing to provide data without being served with a warrant? Unless taking the information is in violation of privacy laws, what's to keep a police officer from using that? (Call it an "informant" if you wish to equate it with similar non-electronic situations.)