A system can receive a request for a transport service from a first device. The request can include a user identifier associated with a first user of the first device, contact information associated with a second user, and a pickup location information. The system can make a determination whether a user account associated with the second user is stored in a user database using the contact information in the request. Based on the determination, the system can select a messaging protocol to transmit data to a second device associated with the contact information. The system can transmit a message corresponding to the transport service to the second device using the selected messaging protocol.