Apple is looking for people who are good at telephony software. Maybe too good. In fact, some are suggesting that perhaps Apple is planning on launching its own mobile voice and data infrastructure, thus eliminating the need to sell iPhones through Verizon, Sprint, or AT&T and potentially flip the mobile carrier market completely on its head. All this from a couple job postings. But when it comes to Apple, we expect grand speculation based on small evidence.
Then again, there are some level-headed analyses of what these job listings could mean as well. For example, it's no secret that Apple probably has a very tight relationship with AT&T, and now Verizon and Sprint as well, and in all likelihood they work very closely together when developing new products or services. So having people on the Apple team who are well versed in the systems and services that mobile carriers use is certainly an asset.
On the periphery of all of this is that Apple wants to strengthen its position in the world of voice-over IP. So while it's probably unlikely that Apple has any designs to overthrow AT&T, it's very possible that the company wants to give Skype a run for its money. Services like FaceTime already compete for the connected consumer who wants to chat with someone without using traditional phone services, and if Apple can expand that into something more universal, it might have a shot.