https://docs.google.com/forms/d/e/1FAIpQLSfVAmZnAqrYzIjfwPxgk_IChzu2wMW2MSCt5TsNkXJD6fYzuQ/viewform

"A telephone number is a sequence of digits assigned to a landline telephone subscriber station connected to a telephone line or to a wireless electronic telephony device, such as a radio telephone or a mobile telephone, or to other devices for data transmission via the public switched telephone network (PSTN) or other public and private networks.

A telephone number serves as an address for switching telephone calls using a system of destination code routing."

[https://en.wikipedia.org/wiki/Telephone_number]

Thus, a telephone number uniquely identifies a device, the target device, to which one might wish to send a text (SMS) message.

"Short Message/Messaging Service, commonly abbreviated as SMS, is a text messaging service component of most telephone, Internet and mobile device systems. It uses standardized communication protocols that let mobile devices exchange short text messages. An intermediary service can facilitate a text-to-voice conversion to be sent to landlines....

The service allows users to send and receive messages of up to 160 characters (when entirely alpha-numeric) to and from GSM mobiles. Although most SMS messages are sent from one mobile phone to another, support for the service has expanded to include other mobile technologies, such as CDMA networks and Digital AMPS."

[https://en.wikipedia.org/wiki/Telephone_number]

Thus, SMS allows sending a text message of up to 160 characters to a target device via the target device's uniquely identifying telephone number.

Scope:

A cellphone is able to send a text message of up to 160 characters to a target device identified by a telephone number.

A cellphone is able to receive a text message of up to 160 characters from a source device identified by a telephone number.

A cellphone that has sent a text message to a target device receives an acknowledgment when the sent text message is delivered to the target
device.

Additional Requirements to Categorize as D or G w.r.t to the scope. [**** These are somewhat ordered, but we can shuffle them in any questionnaire.]

1. A text message can be sent to a set of telephone numbers.

2. A text message can be of any length (not just 160 characters).

3. A text message can be an image.

4. A text message can be a file of any format.

5. An arriving text message shows the text message's sender's phone number and arrival date and time.

6. An arriving text message shows the text message's sender's phone number and sending date and time.

7. The acknowledgement of delivery of a text message shows the text message's recipient's phone number and arrival date and time.

8. If the target device of a text message is a cellphone, use the SMS network for transmitting the text message.

9. If the target device of a text message is a landline phone, use the PSTN for transmitting the text message.

10. If both the sending cellphone and the receiving device of a text message are currently connected to the Internet, use the Internet for transmitting the text message.

11. Pair a cellphone being used to send and receive text messages with a computer so that the computer's message app can send and receive text messages via the cellphone, as if the computer were the cellphone; the text messages are stored in the cellphone.

12. If the phone number to which a message is being sent is not well formed, don't transmit the message and inform the user.

13. If the phone number to which a message is being sent is not associated with any device, don't transmit the message and inform the user.

14. If the target device is not capable of receiving text messages, don't transmit the message and inform the user.

15. If the target device is shut down, then delay the transmission until the device is back on.

16. If the transmitting message rejects a text message for any reason, e.g., the message is too long, inform the user.