About the meaning of function: I would advise you to read these two papers:

http://www.nature.com/nature/journal/v489/n7414/full/nature11247.html

and

http://gbe.oxfordjournals.org/content/early/2013/02/20/gbe.evt028.full.pdf+html

Introns are generally considered as "non-functional". However, some of them display sequences involved in alternative splicing and others enhance gene expression (see http://onlinelibrary.wiley.com/doi/10.1046/j.0960-7412.2001.01192.x/abstract;jsessionid=8B97947ACDEDA381FB99FF7F870D7DFD.f02t01)

Best,

As Yann alluded to, the answer to this question really depends on your definition of the words "junk" and "function". While the introns may not carry any information carried over directly into the amino acid sequence of translated proteins, that does not necessarily mean that they did not contain any information as their sequence may provide docking sites for various DNA-interacting proteins and, at the very least, the presence of introns has an influence on the higher-order structure of DNA, the rate of transcription, etc. ... so, in short, I'd vote for: "No, they are not junk!" :-)