Save my cellular phone bills

I always buy 25,000 rupiah credits on my pre-paid im-3 card voucher or e-voucher for a month, only for 27,000 rupiah or 2.7 US Dollar (1 US Dollar = 10,000 rupiah). I use this im-3 card from indosat. Because most of my friends use indosat products, before axis (other GSM product) and Esia (CDMA product) came out and become competitor. Axis has claimed itself as cheapest rate on GSM and Esia as cheapest rate on CDMA. And my friends use various competitor products as long as it fits on their budget. Even my mother, Tina and my sister, Rohmah use CDMA product, Esia.
At first, they want me to change my im-3 to Esia to get cheaper rate as the same Esia community. I choose to stay on im-3 because my cell phone number is already recognized by anyone who knows my cell-phone number. Why should I have to buy a CDMA cell phone to migrate from GSM to CDMA? It takes more money to spend to have a new Esia number.
I prefer using Short Message Services (SMS) to voice call to reduce m cell phone bills. Except it is very urgent or emergency call.