Maxis APN
1) Home -> Menu -> Settings -> Wireless & networks -> Mobile networks -> Access Points Name
2) Menu -> New APN
Name = Maxis(3G)
APN = unet
Username = maxis
MMSC = http://172.16.74.100:10021/mmsc
MMS proxy = 202.75.133.49
MMS port = 80
APN type = default,mms
(Others, leave blank)

DiGi APN
1) Home -> Menu -> Settings -> Wireless & networks -> Mobile networks -> Access Points Name
2) Menu -> New APN
Name : DiGi Internet
APN: diginet
MCC: 502
MNC: 16
APN Type: default
(Others, blank)

DIGI MMS
APN: digimms
username: mms
password: mms
Proxy: 203.092.128.160
Port: 80
MMSC: http://mms.digi.com.my/servlets/mms
MMS Proxy: 203.092.128.160
MMS Port: 80
MCC: 502
MNC: 16
APN Type: mms

Celcom APN
1) Home -> Menu -> Settings -> Wireless & networks -> Mobile networks -> Access Points Name
2) Menu -> New APN
Name : Celcom 3G
APN : celcom3g
MMSC: http://mms.celcom.net.my
MMS Proxy : 10.128.1.242
MMS Port : 8080

**Credits to Benny888

Congrats..~ =)

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Added on March 6, 2011, 1:01 am
depends on you whether you want to flash or not. using stock radio can, custom radio also can. but for example you're using RevoHD rom, mike (developer) suggested to use other radio (refer in his thread) because radio effect to network / signal strengh, bluetooth, wifi etc.. for RevoHD, kernel suggested are BUZZ kernel. 

buzz oc 1.6Ghz meaning you can overclock your cpu maximum to 1.6Ghz.. while buzz oc/uv 1.3.5 maximum only 1.2Ghz.

edit:
1.6Ghz gives your DHD more performance.. but your 2nd question i can't anwser, as i didn't OC my DHD to 1.6Ghz.. maximum i set 1.3Ghz only. 

edit 2:
but so far i OC to 1.3ghz, didn't give me any problem yet.   because i frequently monitor my cpu voltage is in good level.

using SetCPU. i think it's not available in Market, so need to manually find it. can search in XDA..

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Added on March 6, 2011, 1:57 am
meaning if the theme can support 3.0 already, so no problem..  sorry if i'm giving wrong info.   

back when i'm using ARHD, i'm also flash to other custom kernel.. and yes, i flash to leedroid kernel + ARHD rom.. from my experience, so-so la instead of Buzz kernel. but yet, no negative effect happened to my phone.

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Added on March 7, 2011, 12:38 am
moderate usage i.e call / sms / games (about 30-45minutes), surfing net, battery can last for 1day 1hour like that.. maybe you can refer to Garage Sales for other extended batteries. i cannot recall, before this someone from garage sales posted his advertisement, selling Andida or something..