WP2248.1 & WP2248.2: SMS Provider(s) for GOV.UK Notify

Description

GOV.UK Notify is a digital communications platform, developed and run by the Government Digital Service (GDS). Notify allows public sector service teams to send notifications (text message, email and post) to their users. 
The notifications are typically status updates, requests for action, MFA codes, receipts of applications or supporting information, and reminders. The messages are sent via an API or manually through a web interface.
Currently there are over 8,700 service teams using GOV.UK Notify, from over 1,500 public sector organisations across central and local government and the NHS. 
Notify sends an average of 3 million SMS fragments a day, regularly achieving peaks of 7 million.  
Many Notify services send messages that are longer than one fragment and the average message sent via Notify is 2 fragments long.  Notify SMS messages have a high average delivery rate of 95.7%.
Notify uses two concurrently integrated SMS suppliers to ensure a resilient service. Typically, traffic is shared between the two based on supplier performance (speed of processing) and load. Ultimately GDS reserves the right to allocate work between suppliers at its absolute discretion and there is no guarantee of volume as it's influenced by both government policy and how the services choose to use Notify.