For not-free iphone applications, can I use sound files from this websites?
Tintagel's Free Sound File Archive
Can I download the wav files and use/play them in my app, without getting into any problems? I just need several very short wav sounds(shorter than 1 second).
Well, the top of the website says that they are provided free of charge, so that would mean they've been release to the public domain and you're fine.
However, the second sentences says "to the best of our knowledge," which implies that whoever made the website did not create the sounds, and might not have the rights to give them away. Given the way it's worded, it sounds like someone just found those sounds and put them up online. I'd look somewhere else if you're worried about the legality; there are plenty of websites that offer media with real, proper free licenses.
The very top of the page says:
To the best of our knowledge, all wave, midi, and audio files presented here are in the public domain and are available for use without restriction.
So, yes, if you trust that.
If you really want to be safe, record your own sounds - that way, you know that the copyright holder has given you permission to use them. Unless you have a blanket release of copyright on those (or other) files, or an explicit licence to use them for any purpose, you can still get into trouble.
And I don't mean something wishy-washy like:
To the best of our knowledge, blah blah blah ...
That's unlikely to hold up in a court of law :-)
The main problem with digital copies is that they're perfect reproductions, meaning the copyright holder can easily tell that you've ripped off their work.
Not that I would suggest this as an option, since it's still probably a derivative work, but if you really can't record your own sounds, you might want to think about editing the sounds somewhat to make that harder, ideally fed from the computer out through a speaker back into a microphone and into another file :-)
Or, look into sites on the web where they actually state that they own the copyright and license you to use the files as you see fit. That way, you at least have some protection if they (or someone else) comes back later to collect payment.
One example is Partners In Rhyme, which has a huge range of effects which they appear to own the copyright to, and with a generous royalty-free licence. This was found as the second entry when googling "public domain sound effects" (this first was a rather useless, content-free tutorial on how to find public domain sound effects). There are plenty of other links bought up that you may wish to check as well.
To be safe, I'd actually print out the licence and screen dump the pages where you're downloading from but that's because I'm inherently paranoid :-)