I don't get 3g In 1 of the 3 carriers in my country.

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Hello,
My sister bought me a samsung galaxy s2 i9100 from Thailand
Its
product code : GT-I9100LKATHL
PDA : I9100DXKF4
PHONE : I9100DXKF1
CSC: I9100OLCKF1

Now I have a very bizarre problem
We have in Israel 3 carriers and

pelephone : 3g-2100 , 850
cellcum: 3g-2100, 850
orange: 3g-2100, 900

Now I can not get 3g in orange.. Only with cellcum and pelephone sim card..
Could it be that my device dont support 2100 ( or maybe its turned off in the modem ?)
like in here
android fourm (cant post links) ... 258859-how-enable-850mhz-3g-network-frequency-your-samsung-i9000-galaxy-s.html <-- I tried it does not work..
But I did not tried to put a different rom..
I dont want to reinstall everything..

Is there a way only to flush the modem????


My big question is .
When I'm connected to 3g Is there a way to know in what mhz am I connected?

If when I put pelephone sim card I'll know what mhz is used to be connected to 3g it will help me Identify the problem...

Thank you

UPDATE
Well I've updated to lite'ning Rom v4.2
Still all I get from Orange is G
Is it possible that the phone does not support all 850/900/1900/2100?
Could it be ?

update

Well its seems that I just had a bad orange sim card it was sim+ instead of usim+

The stupid thing is that In the first time I sow the problem I suspected it was a bad sim card.. I called Orange and the stupid lady told me that My sim card is ok and If I have a problem its in my phone...