When writing applications for software, specifically mobile devices, will there be a problem with using any specific type of fonts (copyright/patent issues)?
If so, how can we avoid this possible problems?
Will it then make a difference if the app was a paid version or a free version?
That depends on the individual font and how it is encoded, then decoded into a human-readible glyph.
The shapes of the glyphs in fonts cannot be copyrighted. If fonts could be copyrighted, then every printed text that was rendered in such a copyrighted font would be a derivative work.
However, the data files that encode fonts can be copyrighted. If you bundle a font with your app, you have to take care to comply with any license terms under which that font is published. If you buy a font for personal use from Adobe, you are not license to redistribute it. I'm sure Adobe is happy to allow for redistribution, but to get licensed for that, you'll need to pay them a lot of money.
Many of the technologies for translating the font data files into the rendered glyphs that you see on-screen are patented. That is not likely to be a problem for you on mobile devices, as the patent licensing is the responsibility of whoever is distributing the implementation of these font-rendering technologies. That's usually the handset vendors.
You will only need to obtain patent licenses if you yourself provide the code that translates a font's data file into a screen glyph. If you are using the type rendering engine that is built into your mobile device's operating system then you don't need to worry about the patents.
Note that source code is not considered to be an implementation of a patented technology. Google doesn't have to pay any fees or obtain any licenses to distribute the Android sources.
That's up to the device vendors, as program binaries ARE considered implementations that are subject to the patent laws. I suspect that many such vendors don't understand that, and that they all figure that Google has licensed all the patents that cover the Android codebase. That would be the case if they were licensing a mobile OS in binary form, but it's not the case when they are just getting source code.
You should be using fonts that are licensed for commercial use. Some fonts cannot be widely used or distributed, depending on the licensing. Read the font license when purchasing or contact the author for information. This may apply to both free and paid fonts.
Fonts are like songs; they are protected by copyright, and you need a license to use them.
If the font license is a free, unrestrictive license, then you probably won't have to pay money to use it. If the font is already on someone's mobile device as part of the operating system installation, you shouldn't have to pay for a license.
If the font is a commercial font that requires you to pay a license fee to use it, then that's what you have to do. Check the license agreement for the font; there should be sufficient information there to figure out what you need to do.
The situation varies per jurisdiction. The font file itself (the binary .ttf, .otf, or whatever format it's in) is generally copyrightable pretty much everywhere in the world, and if you (digitally) convert it to a different format, you are creating a derived work, which is also covered by the original copyright.
The font design itself, however, is a slightly different story. In some jurisdictions, font designs are not considered works of art and are thus not subject to copyright; in others, they are. So if you make a font from scratch that looks like, say, Adobe Garamond, but isn't derived from the actual Adobe Garamond, you may or may not be subject to copyright claims.
And then there's trademarks, another form of intellectual property protection. Again, some jurisdictions allow trademarking entire fonts, others allow trademarking individual glyphs (which gets pretty damn expensive for entire unicode fonts), yet others disallow it altogether.
The safest (and probably wisest) thing to do is to obey the license that comes with the fonts you're using, use a free font (fontsquirrel is full of them), or not embed any fonts yourself.
Fonts are the font SOFTWARE (the actual .ttf or .otf file)
Just like Microsoft Office, only tiny.
Taking a font file and putting/embedding it in software, hardware, on a server, using it with @font face all requires a license fee
Taking the letterforms produced by a font like a .bmp or .jpg or any static picture of text is covered under the general EULA for $30 online at fonts.com, myfonts.com, linotype.com
When shipping the font in your app or serving it up on a server that's where you need an offline license that can cost thousands
