what is the difference between 3510i and 3530?

because when i bought a dual sim for 3510i,some network cannot function properly like the globe network.it wont give any signal but when i used it on a 3530 unit, it works.what is the problem?

i also noticed that when someone calls me on my phone, it will give a feedback.whats wrong with 3510i..

pls brighten up my mind?