An interesting anecdote that speaks to this question:
My cottage in Eastern Ontario has no Rogers coverage. Excellent Bell/Telus coverage in the area. Whenever friends/family visit with Fido phones, a Rogers "discount" brand, their phones roam perfectly on Bell's network. Rogers customers get no roaming or coverage. So far no roaming fees have been noted. It seems there can be benefits to using the discount brand that go beyond price.
Professionally, having worked in the industry previously, the only "traffic prioritization" that I'm aware of is reserved for emergency services (police, fire, ambulance, etc). For example, some police forces use cellular networks for their mobile communications (voice and data).
DMX 68' tower, HyGain HAM 5 rotator, Antennas Direct DB8e & C5, Channel Master 7777 preamp, Siemens surge protection. TiVo Roamio DVR