I assume by 2 rings you mean two cycles (ie ring ring, ring ring) because in my experience its perfectly normal for most phones to not ring for 2 rings (caller side), even landline phones. Its simply lag between call initiated and received.

However the N900 does have real problems in PR1.2 with calls. I almost always now seem to get the phone ringing, the screen lights up as I take the phone out of my pocket, then it turns off again and I am left trying to get it to come out of standby so I can answer the call.

Why there is this obsession with NO buttons on touchscreen phones I do not know. I would much prefer it to be like the N97 or 5800XM where you at least have pickup/hangup buttons so you do not have to rely on the touchscreen.