Calls Fail on 4G While Data Works in a Kandhamal Village
A customer in a village about 12 km from a block town in Kandhamal uses a Realme C25 with a Jio SIM. At home the status bar shows 4G with two bars, mobile data runs at 3–6 Mbps, but every outgoing call fails after about 15 seconds and incoming calls go straight to voicemail. The same SIM in a neighbour's Redmi 9A makes calls normally. The customer's phone also makes calls when he travels to the block town. The technician confirms the SIM is recognised, the IMEI is clean, the APN is set to Jio Internet, network mode is '4G/3G/2G auto', and software is updated. In the phone's testing menu, the phone is camped on LTE band 5 with RSRP −112 dBm and SINR 3 dB. The area has no 3G service; 2G is available on 900 MHz from other operators. The customer does not want to change the phone or port the number.
1. Distinguish between an RF coverage problem and a VoLTE provisioning problem using the evidence given.
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Data working at 3–6 Mbps proves that LTE packet data and the IP path are usable, but it does not prove that voice over LTE is usable. Jio has no 2G or 3G fallback, so a call depends on IMS registration and on an uplink radio link good enough for VoLTE. RSRP −112 dBm with SINR 3 dB is marginal: data survives through retransmission, while VoLTE can fail after a few seconds when uplink quality collapses. The fact that the SIM works in the neighbour's phone shows the SIM is provisioned for voice. The fact that the customer's phone works in town shows the phone's VoLTE stack can work. That combination points to a location-dependent RF problem interacting with VoLTE, not to a dead SIM. A provisioning fault is still possible if the phone's IMS settings or VoLTE toggle differ at home, so check IMS registration status before concluding coverage.
2. Propose a three-step diagnostic plan that does not require changing the SIM or the phone.
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Step 1: In the phone's testing menu, check whether IMS is registered and whether VoLTE is provisioned; confirm the VoLTE toggle is on and the IMS APN exists. Step 2: Reset network settings and test at different spots in the house, especially near a window or outside, recording RSRP and SINR each time. Step 3: Borrow a known-good Jio SIM and test in the same phone at the same spot; if calls work with the borrowed SIM, the issue is account-side, and if they fail, it is phone or location. This separates provisioning, handset settings and RF without asking the customer to change number or handset.
3. Recommend a practical solution and explain why forcing 2G-only mode is not appropriate for this SIM.
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Recommend Wi-Fi calling if the handset and operator support it, because a broadband connection would bypass the weak outdoor signal. Otherwise, identify the best indoor spot or use an external antenna-friendly location, and keep the phone on VoLTE with IMS registered. If coverage remains unusable, advise a different operator that has 2G or 3G fallback, or a fixed-line solution, while explaining that the customer's refusal to port limits options. Forcing 2G-only mode is wrong for a Jio SIM because Jio does not operate a 2G network; the phone would lose service entirely rather than fall back. A consumer RF repeater is not a reliable or legal fix in this setting, so do not suggest one as a guaranteed solution.