I think it's too late now.
Computer-controlled speakers are simply ubiquitous in 2017, and an unleashed AI would be a brilliant and relentless hacker, able to take over any device with any published vulnerability instantly, and probably others very quickly. Make sure you're aware of the unbelievable and actual feats of human hackers before estimating the limitations of your AI. An AI would be even better, perfectly diligent, and tireless. With the way we've arranged our world at present, there's simply no way to keep this thing from killing us all.
But, if you roll back to like 1995 or earlier (could be later if you choose a less developed country, but by now even Sierra Leone has too many cell phones to be safe), the conflict could become interesting. One problem for the human team is that the lack of summoning magic is not all that much of an impediment. 115
Humans are easily manipulated. Even after the humans are fully aware of the threat, some of us are craven cowards and could totally be bossed around by our cell phones. The earlier you go, the fewer people are accessible to the AI for extortion purposes, but even if you go all the way back to the 70s, those few who are plugged-in will be well-positioned to do the AI's bidding.
Also, just because the AI begins play as a local entity which could be destroyed doesn't mean it would stay that way. The only excuse for an unleashed AI failing to make redundancies of itself everywhere, preferably before ever revealing itself, is if there's just no other hardware that can handle it. Given the actual successes of distributed computing, again, you'd want to go earlier to make this plausible.
I think 1995 +/- 3 years is the most compelling date to set such a conflict. The humans could destroy communication networks and the regional power grid as a defense, you could have meaningful roles for individual humans in the conflict (your wizard phone might promise you a throne as easily as it could promise you a painful death, and then you would remain the AI's agent and motivated to keep that fact a secret even if you were secure from its threats from time to time.) But there are enough computers and speakers connected to them spread around that the AI could still legitimately pose an existential threat to humanity. 115