Why do contacts in India receive SMS messages from non-numerical SMS codes?
As mandated by the Telecom Regulatory Authority of India (TRAI) and cited in http://www.nccptrai.gov.in/nccpregistry/regulation1diccndiv.pdf (pages 34-35), SMS codes for India must follow a specific format. The first two characters are codes referring to the access provider and the service area, respectively, which must be separated by a dash (-), followed by the six-character identifier of the company or organization sending the message.
A message originating from Everbridge might be received from the SMS code "VM-EVBRDG". In this example, the "V" specifies that the access provider is Vodafone, the service area is Mumbai, and the company sending the message is Everbridge. For a list of the codes used to identify access providers and service areas, please see the following article: https://www.smsgatewaycenter.com/updates/list-operator-codes-sms-sender-name/.