There are several sets, from several artists, belonging to the LPC collection. Most are released with more than one license. You can use any of the available licenses. What you need to do to be in compliance depends on which license you are using and, to a lesser extent, which author produced the particular set of LPC assets you're using.

Most of the LPC stuff is licensed CC BY-SA and GPL, and most of the original stuff is from Sharm and Redshrike. There are other submitters, but those are the two most prevalent LPC artists. 

So, to narrow down the answer, which specific collections are you planning to use (link?) and of those collections, which license do you plan to use?

Hate to toss cold water, but most likely the works you are thinking of using use either the cc-by or cc-by-sa license, both of which can not be used with iOS apps due to their 'anti-DRM' provisions.

MedicineStorm is right though, can't say for sure without knowing the exact works and licenses.   I do encourage you to look into this so you don't end up using a work in a way that violates it's license.

Well, that is true for most other cc-by licensed works, but Sharm and Master Redshrike gave an anti-DRM waiver for all their CC-BY LPC stuff. Thus, my statement about...

"... compliance depends on ... to a lesser extent, which author produced the particular set of LPC assets you're using."

Yay! :D