My case:

Port to Celcom First gold.
hoping to receive offer from maxis, missed their call.
Unable to call back. Seems like that number only for them to call out.

Hence I'm on celcom now.

My review:
Maxis 4g still the best. More stable and faster. I was at KLCC area and Puchong Kinrara. However, still satisfy on overall network quality on celcom