T-Mobile has sent out the invitations for its Un-carrier 5.0 announcement June 18. The event in Los Angeles comes with few details; just a tagline reading “We don’t play it safe and sound.”

Considering T-Mobile’s recent VoLTE launch in Seattle and using “sound” as a clue, the upcoming announcement may have something to do with the HD Voice-enabling technology. A June 18 national rollout for VoLTE would likely be soon enough to make it the first U.S. carrier to do so.

AT&T recently launched VoLTE but for its coverage is limited to select markets. Verizon has promised to rollout VoLTE nationwide later this year. And Sprint, with no VoLTE plans yet, continues to turn on HD Voice in additional markets.

T-Mobile-owned MetroPCS launched VoLTE back in 2012 so that gives the carrier a strong starting point. And, as CTO Neville Ray pointed out in a recent blog post, T-Mobile last year launched HD Voice without VoLTE.

T-Mobile’s new VoLTE launch is using LTE-Advanced technology called Enhanced Single Radio Voice Call Continuity (eSRVCC) in hopes of providing more stable connections when moving between the carrier’s networks.

Of course, this is just conjecture and T-Mobile could have something completely different up its sleeves.

T-Mobile’s previous Un-carrier initiatives have seen the company do away with two-year contracts, offer an early device upgrade program, offer free international data roaming and promise to pay off ETFs for customers switching from other carriers.