Blackberry maker Research In Motion Ltd suffered service problems in Europe on Friday, just as its key rival Apple Inc started deliveries of its new iPhone around the world.
"Some users in Europe, Middle East & Africa are experiencing issues with their BlackBerry service," the Canadian firm tweeted from its British twitter account.
Vodafone Plc said some of its clients were facing the problem and that RIM was working to fix it.
Last October a system-wide failure of the service left tens of millions of frustrated BlackBerry users on five continents without email, instant messaging and browsing.
It took days for RIM's chiefs to apologize over the problems and the company's handling of the issue was heavily criticized.
"This is an opportunity to demonstrate that RIM has learnt lessons from last year. If it is handled poorly again, it could see a faster erosion of its installed base," said Canalys analyst Pete Cunningham, acknowledging if problems last just a few hours the impact would be minimal.
Earlier this week some customers of T-Mobile, the fourth-biggest U.S. mobile service provider, faced a service disruption that affected emails and internet browsing for some BlackBerry users.
(Additional reporting Sarah Young in London; Editing by David Holmes)