i'm looking for some advice

vodaphone prepaid plans
uniwireless offer

here's my situation: i'm using vodaphone prepaid for my handphone while down under. and the prepaid plan has expired. now i'm looking for a plan to "recharge" my calling credits.

the uniwireless website is offering me 10% discount for whatever plan i choose. it expires 15th may. so i want to choose a plan from there and recharge asap, and get a better deal.

i'm looking at 2 plans primarily(prices are in AUD, but that's not an issue):

• $50 - worth $50 of calling credits, 60 days to expire. costs: $45
  
• $100 - worth $100 of calling credits, 60 days to expire. costs: $90

and then there is the other one which has a catch:

• $49 - worth $230 of calling credits, 30 days to expire.
  

it costs $44.10 for this discount i'll be getting.

my spending so far has been an average of about $60+ a month. which goes to say $50 won't necessarily be enough for a month of my usage. it'll probably be used up sooner. if i get $100, one worry is if i would overspend for the first month and use it all up too soon. or would i not be able to spend it all by the 60th day. but the offer, with its limited period now, i might not be able to get a similar offer next time round. so a $100 plan for $90 would be worth it.

but i'm not sure. i'll hang around a few days more before coming to a conclusion on this one. meanwhile i'll work on my assignment due next monday. and thank goodness this is the last one of its kind! for this particular subject that is...