Intelligent communication line selection supporting rich context of input factors

1. A method implemented at least in part by a computing system, the method comprising:

selecting a first default communication line;

displaying a user interface depicting a plurality of contact points for a contact and an activatable user interface element initiating communications with a particular contact point for the contact;

receiving an activation of the user interface element;

responsive to activation of the user interface element, initiating communications with the particular contact point via the first default communication line; and

for another of the contact points of the contact, presenting a second, different communication line as a default.

2. The method of claim 1 wherein:

the first default communication line is provided via a first non-subscriber identity module communication service; and

the second default communication line is provided via a second non-subscriber identity module communication service different from the first default communication line.

3. The method of claim 1 wherein:

the first default communication line is a first communication line selected from a subscriber identity module line and a non-subscriber identity module line; and

the second default communication line is the other of the subscriber identity module line or the non-subscriber identity module line.

4. The method of claim 1 wherein:

selecting the first default communication line comprises selecting a communication line most recently used for the contact.

5. The method of claim 4 further comprising:

propagating the first default communication line to a different contact point for the contact.

6. The method of claim 1 wherein:

selecting the first default communication line comprises selecting a communication line involving communication activity with the particular contact point.

7. The method of claim 1 wherein:

selecting the first default communication line comprises selecting a communication line on which an incoming message was received from the particular contact point.

8. The method of claim 1 wherein:

selecting the first default communication line comprises selecting a communication line based on a source account from which the contact originated.

9. The method of claim 8 further comprising:

determining that communication activity with other contacts originating from the source account is predominantly conducted with a particular communication line;

wherein selecting the first default communication line comprises selecting the particular communication line responsive to the determining.

10. The method of claim 1 further comprising:

determining that communications in a particular time period are conducted on a given communication line; and

selecting the first default communication line comprises selecting the given communication line.

11. The method of claim 1 further comprising:

determining that a last name of the contact matches that of a device user;

wherein selecting the first default communication line comprises, responsive to determining that the last name of the contact matches that of the device user, selecting a communication line associated with personal activity.

12. The method of claim 1 wherein:

the user interface comprises a label of the first default communication line proximate information for the contact.

13. The method of claim 12 wherein:

the label of the first default communication line is displayed as part of a communication line indicator-switcher user interface element collection.

14. The method of claim 13 further comprising:

receiving an indication to override the first default communication line via a user interface element in the collection.

15. The method of claim 1 further comprising:

overriding the selected first default communication line based on signal strength associated with the first default communication line.

16. The method of claim 1 further comprising:

overriding the selected first default communication line based on content of a message associated with the contact or particular contact point.

17. The method of claim 1 further comprising:

overriding the selected first default communication line based on do not disturb functionality.

18. The method of claim 1 further comprising:

overriding the selected first default communication line based on billing arrangements.

19. A mobile device comprising:

one or more processors; and

memory coupled to the one or more processors, wherein the memory stores computer-executable instructions causing the mobile device to perform a method comprising:

selecting between a subscriber identity module (SIM) line and a non-subscriber identity module (SIM) line as a default line;

displaying a user interface depicting a plurality of contact points for a contact and an activatable user interface element activatable to initiate communications with a particular contact point for the contact;

receiving an activation of the user interface element;

responsive to activation of the user interface element, initiating communications with the particular contact point via the selected default line; and

for another of the contact points of the contact, presenting a different subscriber identity module (SIM) line or a non-subscriber identity module (SIM) line as a default line.

20. One or more computer-readable storage media comprising computer-executable instructions causing a computing system to perform a method of selecting a default communication line for a contact point associated with a contact, the method comprising:

receiving a plurality of input factors comprising a source of the contact point;

selecting a default communication line for the contact point based on the source of the contact point, wherein the selecting further supports factors comprising a communication line with which the contact point is registered, a communication line from which the contact point was imported, and a communication line most recently involved in communications activity with the contact point; and

subsequently overriding the default communication line selected for the contact point, wherein the overriding supports factors comprising explicit selection received from a user interface and signal strength.