GSM Antenna Selection

My country (GR) uses 900/1800 based on GSM World Coverage Map- GSM Country List by frequency bands
I use the SIM800L module for SMS only and maybe in future for 2G.

I would like to increase the poor signal on remote locations.
Probably I need high gain, right?
I'm not familiar with dbi, so I would like to help me, if the following is ok

Band 900 Mhz / 1800 Mhz 3dBi Omni Directional Magnetic Antenna GSM DCS Cellular Aerial 3m Cable with SMA male Connector

It will be placed on mountains with poor signal