The Ministry of Defence spent £6.6m on mobile phones and contract charges for ministers, members of the armed forces and civil servants last year.
In a parliamentary written statement the Defence Minister Andrew Robathan said more than 45,000 phones had been issued to staff.
"Official mobile communication devices are provided for the conduct of business in a similar way to desk-based telephones, a computer or a laptop. Technology-enabled mobile working helps increase our efficiency, support flexible working patterns and drive down administrative costs," he said.
Of seven department ministers questioned, the Department of Health was found to be the biggest spender on mobile communications for department officials alone, totalling £738m last year. This averaged £424 per user, the second highest cost per head.
The Scotland Office was found to have the highest average user cost of £472 for its 27 officials issued with devices, while department of Communities and Local Government had the lowest spend per head of £158 each user.
Total mobile phone spend per department:
Total - £6.6m
Average user spend - £145
Department of Health
Total -£738, 301
Average user spend - £424
Department for Transport
Total - £300,246
Average user spend - £203
The Department for International Development
Total - £222,789
Average user spend - £306
Department for Communities and Local Government
Total - £113,000
Average user spend - £155.8
Northern Ireland Office
Average user spend - £268
Total - £12,757
Average user spend - £472