Looking at 2degrees plans it will cost
$39 per month plan -S3 $799
$799 if you go on a 24 month contract at 39 per month (plan im already on) but I could get one on tradme for the same money so no real benefit there Im guessing and no 24 month contract needed.
$89 per month plan -S3 Free
To get it free starts at $89 per month for 24 months.
So thats spending $2100 over 2 years and getting a $800-$1000 phone free.
$2100 total spend over 24 months subtract the free phones value at $799 leaves spend of $1301 over 24 month contract which gives $54 per month.
This doesn't seem too bad, $15 increase p.m over buying outright on trademe or on a $39 p.m plan.
Good way to get the phone if you dont want to pay up front for it.