I am always skeptical on the build quality of china made phones, some doesn't follow 3GPP specification and some brand have weaker antennas than other brands. I have seen some so called "branded" china phones which receive signal 50% weaker than iPhone and Samsung.

So long as other brand like iPhones or Samsung have no issue, I don't think it is Digi's problem.

iPhone and Samsung are widely popular is not without a reason. Intensive RnD and paying copyrights to use telecom patent and chipset so that quality is good and technically compatible with operator's transmission equipment.

If issue persist, just change phone la