What does Dual SIM Standby and Optional Dual SIM mean?

[eureka]

Please see the photo.

*i.imgur.com/cfv8Lym.jpg

May I know what Dual SIM standby mean? I don't have a dual SIM phone, nor have any plan to get one either, just asking this for a friend of mine. He is wanting to know whether both the SIM cards will be active and able receive phone calls or not. Cause on older days there were some Nokia phones which didn't keep two SIM cards activated at same time, and he wants to avoid something like that.

Also, what is the meaning of Optional Dual SIM?

Cheers.

 

[coderunknown]

optional = available in both single and dual sim variants. usually in the US/EU market it'll have single sim whereas in Asia it'll have dual.

dual standby is basically 2 sims being active at the same time. then there is dual active i.e. you can receive calls on both sims at the same time (one call will be on hold). almost all dual sim mobiles are dual standby with only a very few selected ones being dual active.