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You can use tasks with the state set to TODO for this. That also means that ticket/change/problem templates can have multiple TODO tasks added. You can click the checkbox on the TODO tasks to mark them as DONE.
Tickets can be imported using the GLPI API.
ChromeOS supports Android apps and there is an Android agent. I've not personally tested if it works though.
This was added in GLPI 10. You can hold the ctrl key down when clicking on the column headers to add additional sort levels.
It is currently possible to do this indirectly using SIM cards.
For direct linking, see:
Done/WIP for 10.1.0.
The search option exists. If you open the search option dropdown and search "Description" it shows up as Followups > Description.
Customer support service by UserEcho
This is already possible by adding "Assigned to a supplier" as a hidden field in the ticket template (Templates button at top of ticket pages).