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This is what a person should know and do before subscribing to a celco plan; .......
From the opensignal website, overall best celcos are the Big 3 pioneers, ie Maxis, Celcom and Digi. For best rural coverage, it is Celcom, a GLC. The smaller newcomers have good coverage and service in mostly urban areas, ie UMobile, YES and TM Unifi Mobile. Yoodo, XOX and Tunetalk are MVNOs which lease lines from the Big 3 celcos.
1) Research for the best and suitable offer from celco, eg prepaid or postpaid, data quota or unlimited data, limited speed or unlimited speed, move around alot?, etc.
1.1) Check the 4G LTE frequency Band support for both your phone and your chosen celco, eg most mid-end to high-end Android 8.0 or later phones support all the LTE Bands, U Mobile supports only LTE Band 7/2600MHz, Band 3/1800MHz and Band 1/2100MHz, TM Unifi Mobile supports only LTE Band 5/850MHz, Band 38 and Band 40, etc. Other celcos may use different 4G-LTE Bands, eg Band 8 by Maxis. Low-end Android 8.0 or later phones may not support a few 4G LTE Bands.
2) Check the 4G/3G coverage map for your chosen celco at their websites or at nperf.com.
3) Best to buy a RM10 disposable prepaid Starter Park to do actual speedtest at your various frequented locations for a few days.
Eg got 1 TM Unifi Mobile postpaid unlimited-data RM59 promo with 1-year-contract subscriber did not do this test in April 2020 and later found out his house location could not receive 4G Internet data but could only make 3G calls/SMS. TM diagnosed his problem to be a large highrise building near his house blocking the 4G cell signals.
....... Got another subscriber was given a free mandatory cheaper (than Maxis) postpaid U Mobile plan by his employer/company but his house has no to little 4G coverage but could still make 3G calls/sms.
Note that a 4G/3G cell tower has a range of up to 3 miles/5km for Internet data and up to 20 miles for voice calls/SMS. Today, most Internet data runs on 4G while most voice calls/SMS still run on 3G/2G. Ensure you have 4G network coverage for Internet data from your preferred celco.
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i can on attest to phone weirdity.
i got 2 prepaid Unifi Bebas..
Both phone side by side at same location....
My Guess Phone also play a major part even if opensignal say excellent signal...