VC is just not necessary, by any means. I actually wrote an essay as to why a while back, but I'll sum it up.
Splatoon's gameplay is simplistic and the objective is clear. Splatter the ground, cover it in ink to win. By simply performing an action, you give your team a clear message as to what your intentions are and from that information they can figure out what they should be doing. For example, a teammate's covering the ground, advancing towards the enemy team, and you notice he's far up the map and in a major area of the enemy team's ink. In response, you think, "Oh, there's more ground to cover over there, but it's dangerous! I should go help him."
If you don't happen to have moderate team coordination skills as shown in the example above, or you need to speak to your teammates for serious competitive play, you can chat vocally through Skype, Teamspeak, Curse, Mumble, or Raidcall. If you don't happen to have access to that, then you could come up with a plan with your team, such as using the pings for signals. For example, " X ping means 'Come here, help!' and Y ping means 'Retreat!' ".
If you need VC for regular online matches with random strangers, think again. More often than not, people will not be listening to your words, being so absorbed in the game. And if your voice does reach them, they'll either retaliate or ignore you. And again, as stated previously, your actions speak louder than your words. It's not necessary in anyway, or even optimal in a game like Splatoon. It would ruin the overall online experience, what with ragers, and the music having to drown out every time someone speaks, and the every now and then slightly perturbing 35-year old complaining...
Now think about it, do you REALLY want voice chat?