Basically, I'm on contract and I have around 600 minutes a month, I only got my minutes a week ago and already I've only got just over 350 minutes left so feeling slightly worried this month - It'll be the first time I've ever thought I'm going to run out of minutes. So, I was wondering, I'm sure you could get some sort of booster thing where you pay an extra £5 for just that month to get more minutes? Is that right? Or am I getting confused? Someone explain? Please

There arent any boosters that include minutes to other networks, but you can get boosters to give unlimited landline calls or unlimited calls to T-Mobile numbers. Basically calls are then free and will not come from your mins.
They are a rolling add-on and will continue @ £5 per month until you cancel them. You can have more than one booster at a time if it suits you