Just ordered the Sim.
So when you say buy a voucher what does that exactly mean? Does it mean go to the shop and buy one from behind a counter?
Is a Top up different than an addon?
I'm a bit confused since I've only ever had monthly contracts since the early 00s.
Next time you're in your friendly local supermarket just buy say a £10 three topup voucher.
When you have the sim installed and activated, which can be a bit of a faff first time if I'm honest, then I would suggest doing it this way (this is how I always do my topups so there's never any payment mechanism linked to the sim...but I'm an anal old flatus). Turn off wifi and turn on using the sim for data, open your friendly browser and login to your account on three, as it's doing it through the mobile data connection you shouldn't need to enter your password details, it should 'auto detect' it's a three sim and route you to the allowances for that specific sim. Now add credit and there's an option to 'use a voucher', enter the voucher number and it should hopefully take the credit info added, the website will then 'invite you' to buy either data addons or minutes addons (these are effectively mini bundles THAT DO EXPIRE even if not used, so don't buy them), instead just leave the credit on the account. Then check the data allowance from your login menu and you should see the screenshot I uploaded earlier.
Although there's a LOAD of absolute nonsense comments it's worth googling "hotukdeals 200mb three sim" and reading the threads. For the avoidance of ANY doubt....
This sim can be used for both data and normal calls
This sim is NOT designed for tablets only (see above)
This sim does NOT automatically expire your credit (see my screengrab earlier)
This sim can be activated fine (read the delivery paperwork properly and carefully, don't just rush in), but sometimes takes a couple of attempts (JUST MAKE SURE YOU DON'T FALL INTO THE TRAP OF BUYING ADDONS THAT ARE TIME EXPIRED..DO NOT BUY ANY ADDONS, they're not needed).
My personal advice, but your choice, DO NOT TOPUP USING A CREDIT OR DEBIT CARD VIA THE WEBSITE, that then ties a payment mechanism to the sim, always use a voucher as the credit never expires anyway, then there's no possibility of arguments later.
I, right now, have a three sim as my backup sim in my primary phone and also in 6 samsung tablets, all of which can make calls, the tablets are used as front ends to my smart house control devices so some are in fixed locations.
Hope this helps.