1 - No one SWIMs here, dont fucking do it it's annoying
2 - If you're dumb enough to have weed, acid foils in your mums car, you deserve to be caught. Use anything in a nice secure environment, or you are just asking for trouble.
3 - No one on here can give you legal advice, best bet it to speak to the best lawyer you can find, and see what happens.
IMO, if you are a cleanskin (never been in touble before), you will get a slap on the wrist and told your a naughty boy and to go and plant flowers on a round about for a couple weeks. If you have a rolling list of similar offences, be prepared to get a short custodial sentence (somewhere between 2 weeks - 2 months), as an attempt of the Aussie justice system to rehabilitate you.
Regarding a warrant, excuse my rudeness, but SWIM (ie YOU), is a fucking idiot. They cant approve or apply for a warrant over the phone in ANY circumstance. If this was the case, it would happen every day. All warrant are approved by a magistrate, I recommend you read up on law and rights if you feel like driving around with naughty things on you. Mentioning mummy, and giving a sob story, will just make the cops a lil more cheeky. They love games and can spot a dumb fuck a mile away and play the game VERY well.
You seem to have been caught with a TINY amount (depending if the tests the tabs for a per mg readingor not), so in MY HONEST OPINION, you will have a fine (if the charge is simply for posession), perhaps community work, and a conviction,
Sorry for the blunt reply, it burns me up when I read of see people doing careless things! GOODLUCK and BE SMART!