Nowadays, most mobile phones can use dual telecom mobile phone cards, including several Apple iPhones that support dual SIM cards. However, the prerequisite is that both telecom cards have the VoLTE function enabled. In the past, dual-SIM mobile phones did not support inserting two telecom cards at the same time because Qualcomm's CDMA patent fees were too expensive. Two SIM card slots required two CDMA patent fees. Mobile phone manufacturers could not afford this cost. In addition, there are relatively few users who use two telecom mobile phone cards at the same time, so old models of dual-SIM mobile phones do not support the insertion of two telecom cards at the same time. If they are forcibly inserted, one number will inevitably be disconnected.
However, starting in 2018, China Telecom began to fully use VoLTE high-definition voice network and slowly got rid of its dependence on CDMA. Telecom mobile phones in most cities across the country now use VoLTE for voice calls. The so-called VoLTE is to deliver voice functions on the 4G network, and 4G does not include CDMA technology. Mobile phone manufacturers do not need to pay additional patent fees to Qualcomm by adding VoLTE functions to both SIM card slots. Therefore, mobile phone cards with VoLTE function enabled, plus 4G/5G mobile phones supporting dual-SIM VoLTE function, all support dual telecom mobile phone cards. At present, Huawei's flagship phones, such as Huawei Mate 30, Huawei P30, Honor V30, etc., are doing better in this regard. They all support dual-card VoLTE, so two telecom mobile phone cards can be inserted at the same time. In addition to Huawei, Xiaomi, OPPO and other mobile phones after 2019 basically support this function.
After upgrading to iOS 12.2, Apple mobile phones also support the telecom VoLTE function. Therefore, dual-SIM Apple phones such as iPhone XR, iPhone However, if an Apple phone uses dual SIM cards from China Telecom, you need to find "Cellular Mobile Network" in the settings options, turn on the "Cellular Mobile Data Options" for both mobile phone cards, and then click "Enable 4G". After entering the enable 4G page, click from? The data only option is changed to voice and data, and both cards can use China Telecom's VoLTE function, thus realizing dual telecom cards. In addition, a problem with dual telecom cards implemented through the VoLTE function is that in places where there is no telecom VoLTE signal or only 3G signal coverage, one mobile phone card will be disconnected. Although this situation is relatively rare, it can still be encountered in some remote areas or subways or underground garages. Therefore, users who use dual SIM cards of China Telecom should still put the main mobile phone card in the main card slot and use the CDMA network if necessary. The non-mainly used mobile phone cards are placed in the secondary card slot, so even if there is no signal occasionally, things will not be delayed.