SEM..!?? I take it you meant SME  o_O
Since you just bought it 2 days ago then i'm sure the warranty from SME is just 1 year. Only SEP gave 2 years warranty before this but it stop giving extra wsrranty since end of last year.
SenHeng/SenQ might give your extra warranty BUT it will be from SME only 1 year + whatever extra year from SenQ itself.
Hope this help :-)

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Added on February 9, 2012, 6:39 am

Do you have any crack apps in your phone?
Do you use sdcard?
- Uninstall any pirate apps from your phone.
- Unmount external sdcard from your phone and see if your problem solve.

I'm using a non-G version and have no problem of laggy or crashing when surfing.
Do you have any pirate apps? A lot of pirate apps can make your phone freeze and hang. Try uninstall it :-)
What you should do is this :-
1) Uninstall all pirate apps.
2) Unmount you sdcard.
3) Do a hard/factory reset.
Then try use your phone without sdcard for a few days. If your phone still freeze or random reboots then it's better you bring it to service centre.

I use to tweak conservative to perform but meh.. better off using ondemand.

Better wait for S3 not much choice right now that is similar or better than S2.

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Added on February 9, 2012, 7:37 am
Redpill is kernel woh. Got init file meh?

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Added on February 9, 2012, 7:42 am
Stock browser dun think got this function. But other third party browser got this option.

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Added on February 9, 2012, 7:43 am
Does it hang at certain apps only? Do you use any task killer?

You mean your device only hang when using stock browser? Try clearing data of stock browser. Try using third party browser to see if there is any issue.