One of the big issues with Voice-over-LTE (VoLTE) goes beyond pure technology, because making IP voice communications work like today's standard cellphone or landline call will require that operators co-operate. That is, they will have to create SIP interconnects between their separate networks to make calls across the different U.S. operator networks. They will have to strike LTE roaming deals to allow international LTE calls. When you recall that AT&T Inc. and Verizon Wireless -- the two biggest LTE operators in the U.S. -- still haven't struck an LTE roaming agreement yet, you can see how things could get awkward. I would think that user expectations around how a phone call should work will mean operators will interconnect their networks sooner rather than later. When I asked about roaming on Tuesday, however, a spokesman for AT&T wouldn't say anything beyond the fact that the operator is launching VoLTE in 2013. We can already get a glimpse of what VoLTE networks might look like without interoperability. When Sprint launches its HD Voice service in the second quarter, users won't be able to place HD calls cross-country, nor will the technology work across different network suppliers' equipment. These technology and co-operative issues are probably part of the reason that VoLTE seems to be taking so long to arrive. There are a lot of moving parts to juggle. I would be mildly -- but not totally -- shocked if VoLTE didn't run across different networks ASAP after the major launches happen in 2013 and 2014. I say "not totally" because I remember how long it took carriers to open up text messaging between networks in the U.S. Of course, the technology challenges could still trip operators up, too. In this day and age though, keeping VoLTE shuttered would be like handing even more users over to the over-the-top messaging apps that already thrive on operators' networks. So, I've asked the GSMA for more information on VoLTE interconnects, and I'll keep an eye on how this all develops. — Dan Jones, Site Editor, Light Reading Mobile