Registering client computing devices for online communication sessions

A registration server to register multiple client computing devices for an online communication session, the registration server comprising:

• an SMS (short message service) transit interface, to receive a registration request message from an SMS transit device that receives SMS messages from multiple client computing devices, each registration request message including:
• a device specific identifying token that is unique to a client computing device of the multiple client computing devices and contains information to allow a push notification service to locate and transmit push notification messages to the client computing device, and a phone number of the client computing device, the phone number determined by the SMS transit device;
• and
• an association module, to generate an association between the device specific identifying tokens and phone numbers, the association to uniquely identify the client computing device in an online communication session network, and to store the association in a registration data store.

A non-transitory machine-readable storage medium that provides instructions that, when executed by a processor, will cause said processor to perform operations for registering a client computing device for online communication sessions, the operations comprising:

• receiving a message, the message including a device specific identifying token that is unique to the client computing device and contains information that allows a push notification service to locate and transmit push notification messages to the client computing device, and a phone number of the client computing device, from an SMS (short message service) transit device that received an SMS message having the identifying token from the client computing device, the SMS transit device having determined the phone number of the client computing device using the identifying token;
• generating an association between the identifying token and the phone number, to uniquely identify the device in an online communication session network;
• and
• storing the association in an online communication session registration data store.