LG G2 (Sprint)
There are also versions of the G2 for AT&T and T-Mobile, and a global version.
Well my real question is does it have a sim slot ?
Are you sure that's the right question? Having a SIM slot doesn't mean much of anything. It doesn't mean a phone has GSM; it might be just LTE. It doesn't mean it will work with your SIM; it may be locked. And even if it's GSM and unlocked, it may not support the 3G WCDMA bands of the network you want to use it with.
Is it GSM ?
Yes, but as another poster stated that might not be the question you need to ask.
The phone by default will support Sprint's CDMA and LTE networks, but may not support GSM out of the box (and if it does, it may be restricted to European frequencies). You would need to contact Sprint to ask about unlocking the phone if you want to use it on GSM networks.
And, to be honest, this model would not be optimal on a North American GSM network-- although it supports GSM and WCDMA frequencies used by AT&T and T-Mobile, it supports none of their LTE frequencies (AT&T uses 700 and AWS, T-Mobile uses AWS only).
A better multi-carrier solution that supports Sprint, AT&T and T-Mobile would ...