Residents rushing to make calls after Tuesday's earthquake jammed phone networks, but no major physical damage to communications infrastructure was reported.
"There appears to be a mass calling event, but we have no reports of damage to our network," said Sprint spokesman John Taylor. He encouraged users to send text messages rather than call, if possible.
Verizon spokesman Ed McFadden also said his company's network became congested but seems to have dodged serious damage.
"Obviously call volume was extremely high in the initial aftermath of the quake, but networks are operational," he said.
And AT&T reported heavy call volume, but no physical damage.
On Twitter, users complained of not being able to make calls on both landline and wireless phones.
Press reports also indicated that 911 call centers were overwhelmed with calls.