[Q] 850 mhz problem

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http://forum.xda-developers.com – hello everybody i am writting from Honduras i am new in this forum and i have some question i have a samsung galaxy s2 I9100, 4.1.2 jelly beans, and i have some problem with the 850 mhz band (2g and 3g).when i put the sim card the cellphone reconigze it but doesnt conect with the network, when i click on "search mobile network", the cellphone dont find the cellphone carrier and this mark (Ø) appears on the corner of the screen i have put some sim cards from anothers company who works in 1900 mhz and there is no problem. help me please (HowTos)