There are several problems there. First you tried +919700751174 (that number can be registered again in 4 days) and then tried +919603172085. Did you change SIM cards? The N900 has to have the CORRECT SIM CARD inserted and you're gonna register THAT phone number! So once you decided which phone number you want to register and have the SIM card of that number in your hand, insert it in your N900, wait 4 complete days without trying, and THEN try the registration again.