Where are the numbers tored on a mobile phone?

[bigsister]

I bought a used mobile from Ebay, and am very pleased with it.
I put in a 'new' sim card from a mobile which I had bought from Argos. Apparently they dont refund on mobiles. But there were numbers stored, and this afternoon I missed two calls. No one yet knows my number, so how can this be? Can numbers be stored other than on the Sim?

[Postdog]

Depends on the phone I suppose. My one you have the option to save to phone or save to sim.

[bigsister]

That might explain it, its an oldish one, a Nokia 3510i. I got it for Mr Bigsister as he finds it difficult to use the ones with small keys.

[good_egg]

when you bought the phone from argos, was the sim card already in the phone? it should have been in an envelope with a tamper proof seal. Numbers can usually be stored in either phone, sim or both, but if youre getting calls and the sim wasnt obviously unused then it sounds like your argos phone had been used before. try looking up the homepage of the network cos most of them offer free sim cards at different times, or speak to customer services and they can tell you if the sims been used before

[bigsister]

Thank you, I'll try that.