The service, which did not require a T-Mobile account, let Facebook users who were online. It was launched on April 20.

On Tuesday, T-Mobile USA notified users through a message on its Facebook page that it was suspending Bobsled.

"We are voluntarily and temporarily suspending the Bobsled service as we work with our partners at Facebook to address their design questions related to differentiating the Bobsled experience from Facebook's own created properties. We apologize for this temporary disruption and are looking forward to expanding the service with other features soon," the message said.

Bobsled let users call any Facebook friend who had a PC with a microphone and headset or speakers. Friends could receive calls even if they didn't have the app. It also allowed a caller to leave a private or public voicemail message. Before the suspension, T-Mobile had said it planned to add smartphone and tablet apps and the ability to make VoIP (voice over Internet Protocol) calls to mobile and landline numbers in the U.S.

In response to a question on its Facebook page, the Bobsled team said it did not have an estimate for when the service would be back but would notify users as soon as it was available.