Hi Tom, I can't tell you exactly as I never really bothered because I had two so when one run out, I could just put in the other. But when I first got one, I registered and it provides a sort of home page with all your info and usage.
They are pretty good as long as yours is unlocked as you can put a cheap local sim in. We used a Nos sims in Portugal which gave unlimited data for 30 days for €30
Where did you buy it? Is it literally as easy as just inserting the SIM card. Do you have to register or anything?
I haven't ever bothered registering my mifi 3 data sims but you can still check the remaining data on the 'My 3' website if you're actually using the internet via the sim you want to query. Look for the green dial 'Data Allowance' logo, click through and there it is. I've also got the 3 app on my iPad for the sim that's in there but it never seems to tally with the website. As others have said, it might not be 100% accurate if you've been using the sim just prior to checking. I'd agree with the suggestion to look on MyMemory for bargains, plus Amazon very occasionally come up with cheaper prices, so worth checking there too.I have the Huawei Wi-Fi E5577C with a 3 12GB data sim, can anyone tell me how to check the remaining data on it, also a good present deal, we will be away after Christmas so could do with another 12GB or above.