Air carrier pilot reported while they were taxiing out of the ramp another carrier entered opposite direction on the same route. Reporter stopped until the other aircraft passed by.

Narrative

At ZZZ after receiving terminal (ramp frequency XXX.XX) taxi instructions to taxi via Taxiway 1 and hold short Taxiway 2X; we came to a full stop short of Taxiway 2X waiting to be able to call ZZZ ground (XXX.X) for additional taxi instructions. When there was a break in communication on the ground frequency; we were cleared to taxi by the ground controller; via taxiway 3; 4; for a departure on XXR/W. As soon as we started to move; a Company X aircraft immediately entered the ramp area; coming the opposite direction; via the path we were to taxi out. Our aircraft immediately stopped. Our sight lines of the Company X aircraft coming south on Taxiway 2 onto Taxiway 2X had been blocked by terminal X from our position on Taxiway 1X. We had moved approximately 5' from the time we had been at a full stop to receive taxi instructions to stopping again to avoid the Company X aircraft. As we were just past the hold short line for Taxiway 2X; there was adequate room for the Company X aircraft to pass our aircraft. It continued past our aircraft; right to left; on Taxiway 2X to their gate. As we had been listening to the ramp frequency before contacting the ground; we were not advised of any entering traffic and we were not told to give way to any inbound traffic. Any communication with Company X on the ZZZ ground frequency was not heard by us; since we had not joined the frequency yet while in the ramp control area; and we were not advised of any entering traffic or told to give way to any inbound traffic with the ground controller once we established communication. (We could not see the aircraft approaching because the terminal structure blocks the view. The ground frequency was also congested as we had to wait for a break in communication on the ground frequency to request taxi instructions once we had joined that frequency.) I believe the ramp controller was possibly not aware of the future proximity of the two aircraft and the ground controller; due to very high workload; was not aware of that as well. The Company X aircraft also did not communicate on ramp frequency (XXX.XX) as it went past our aircraft to the gate. It is possible they were using the other terminal X frequency (XXX.XX) and unaware that they entered a ramp area that required the use of another frequency (XXX.XX). We inquired about the Company X aircraft with the ground controller as it was making a turn into the ramp area from taxiway 2 (transitioning from the ground control area to the ramp control area) and the controller seemed somewhat surprised the Company X aircraft was there when we inquired about desired intentions. I think the worst case outcome for this situation would have been that the two aircraft would have been opposite each other with no way of reversing or maneuvering past the other.