I understand that because of a sudden upsurge in demand for them, stocks of free forces aerogrammes have been exhausted in some isolated areas.
This comprises 20 minutes of telephone time per week; one e-mail per week (which may be increased if operational circumstances permit); and unlimited postal aerogrammes.
However, aerogramme and aerogram may also refer to a specific kind of airmail letter which is its own envelope; see aerogram.
