Masayoshi Son, who is also CEO of a Japanese carrier, says the network quality in the US "is not something you should be proud of," and directly calls out his rivals.
Company reports that its smartphone division also had some trouble in the second quarter as unit shipments fell 3 percent year over year.
After two quarters as the leader of the pack, Apple has dropped to third place in the world's largest smartphone market, says research firm Canalys.
Also coming soon: Skylake, the code name for Intel's sixth-generation Core processor aimed at PCs, is slated to drop during the second half of 2015.
The smartphone giant expects second-quarter operating profit to decline 4 percent and miss analysts' expectations.
The PC maker recorded a net income of $100 million, beating analysts' expectations.
HTC says that its revenue was up 25 percent in the first quarter, but its forecasts are not encouraging.
Given Apple's guidance for the current quarter, Piper Jaffray analyst Gene Munster has boosted his prediction for iPhone sales.
Thanks to its "no device subsidy" model, AT&T says it lost fewer customers to rivals than it ever has in the first three months of the year.
The e-commerce pioneer's overall results hid the differing paths of eBay's two main businesses, with PayPal growing and eBay.com floundering.