sms ur gf a lot & sometimes call/sms other networks.

hmmm...

for prepaid, u can port to umobile, its rm28/month with 500mb (no extra charge) + free 100minutes & 30sms to all networks.
port ur gf to umobile too, so u and ur gf will have free calls for 60mins/day. ur gf no need to use rm28/month but just normal prepaid.

for pospaid, got few options:

(1) port to maxis talk 48. but,
(1a) this plan dont have data plan with smartphone bundle together. so u need to purchase smartphone urself.
(1b) after reach quota, there is additional charges. use apps to shows ur data usage and auto disable once reach quota (purchase additional data to continue, cheaper than PAYU).

so it will be 48 + 18/28/38/48/68 = which is 116 max.

(2) port to digi/celcom, coz their using 1 rate to all networks. the diff:
(2a) digi, if want to purchase bundle smartphone, u need to pay for data (internet) 1st, call/sms/mms is PAYU.
(2b) celcom, u need to pay fixed monthly commitment fee for call/sms/mms + data (internet), extra usage than monthly fee is PAYU, less than commitment fee still need to pay that fee.
(2c) celcom & digi both didnt charged after exceed quota, but will slow down the speed.

digi min is 48, while celcom is 68 (40+28). for celcom smartphone bundle, min is 78 (40+38).

(3) take broadband plan simcard, continue with ur hotlink, and get dual-sim smartphone.
example galaxy y duos, htc desire v, nokia asha 305, csl or china-brand also got.

(4) if, all this time ur cost to call&sms ur gf is at least rm15/month,
then better u convert to postpaid and pay rm15/month for free call&sms with ur gf, by make her as ur supp line.
if u cant afford for her usage (to other than u), then just take new simcard give to her and she use dual-sim phone.

coz celcom supp line is rm15, same goes to digi family prepaid.
digi family postpaid supp line min rm28. while maxis is rm30.

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Added on August 16, 2012, 1:32 amadditional info: all postpaid amount is excluding 6% govt tax