Our IT says
Is that the IT Manager?
If so, you might give up. Even if you can prove the manager wrong, the manager won't be seen to be wrong. If it's a single individual, also known as 'our IT' then your cause may be just as fruitless, since bosses sometimes listen to the 'IT' over all others with matters relating to IT (not so silly all the time).
It might help if you can explain why you think 3G dongles are the best solution versus other solutions. What's the setup, and is your solution more practical, less costly and of more value to the company than other solutions?
Have you produced a report to this effect? Would you?