can anyone or maybe all the sifus help me on this.

i still wanted to know what the culprit on drop calls.
lately, i got alot of drop calls. people cannot reach me and i cant reach people. can the sifus here explain more about this? please..
i heard ths drop calls can be solved by changing the simcard to 256K sim card? how far is this true? clarification needed.

one more thing, i dont know is this a bug from 3.1.3 update or not.
but sometimes when messages come, there's no sound come out.
suddenly see the phone got message. this happen since i update 3.1.3.
kena few times d. around 3 times. anyone experience it before? whats the culprit? 3.1.3 or not?

thanks in advance.
peace.