There are two ways to write IPA symbols in LaTeX. One uses regular pdfLaTeX and the
tipa package; the other uses XeLaTeX or LuaLaTeX and you can enter the symbols directly into your source, assuming you have the correct fonts.
The SIL Doulos font is an excellent Unicode IPA font that is widely used in Linguistics. You can download it here.. But many other OpenType fonts have a full set of phonetic characters too.
I'll outline both techniques here:
Using XeLaTeX or LuaLaTeX
There are advantages and disadvantages to each method. The main advantage of the XeLaTeX/LuaLaTeX route is that your source code becomes much more readable. The downside of this, however, is that you need to develop techniques for entering all the characters, which isn't necessarily fast. However, if you are already used to the TIPA input method (or have existing documents) the
xunicode package (which is loaded by
fontspec) allows you to use most (but not all) TIPA input methods as well, so for many kinds of input you can have either.
The TIPA method allows for a faster input method at the expense of less readable source.