As I understand, a mobile/cell phone, in the standby mode, listens to some kind of circular buffer in its memory for acquired packets from the antenna to check if there's something that regards installed SIM card. What is the rate at which the CPU fetches and checks the packets if there's anything (an incoming call, a text message) that's been sent for the installed SIM card?
The rate at which a mobile/cell phone listens for an incoming call or a text in standby mode?
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I am currently working on a GSM connected device and I feel like I have something to contribute, although I am no expert so be sure to do further research if this doesn't satisfy.
The GSM module I am working with states something along the lines of this in its datasheet (re-worded for NDA purposes, and to make it more general):
A SIM detection pin must be used in order to comply with the 3GPP TS 11.11 document recommendation if the physical design of the mobile equipment allows the user to remove the SIM card during operation.
I combed the mentioned 3GPP document and did not find much talking about this so I am unsure of how well this is specified or if that point was from an older version of the document. Section 11.2.8 "SIM Presence Detection and Proactive Polling" of that document defines a polling procedure to detect SIM removal but only at critical times (what they call "card sessions", for example a phone call).
In any case, my theory is this: this is done as a design decision to simplify the phone firmware, as the phone would only ever need to do its SIM card initialization on power up, and to avoid having to comply with any possible procedures which only apply if you allow the user to remove the SIM card during operation. Seeing as there isn't a clear advantage of providing that feature, it's a no-brainer (for me at least) to go with a design that does not allow SIM hot-swapping.
Your connection to the cellular network, no matter the "G", always uses the same antenna. You can see this in a teardown of whatever phone you have. For instance, here is a teardown of my phone:
In the last photo, you can see that the LTE and EVDO antenna is one and the same. This also handles your 2G connections as well even though they all operate on different frequencies:
What you are doing when you disable your data, is shutting off the modem in the chip that talks on a particular frequency. Each cell phone has several modems. For 2G, 3G, 4G, Bluetooth, etc. Since the "Gs" are similar in the way they operate, they can use the same antenna. Bluetooth and WiFi operate very differently and require different antennas as can be seen in the teardown.
2G connections provide voice and text and, since it's the oldest, has the widest coverage. 3G provides voice (GSM only, see below) and data on the same frequency, and, in some model phones, at the same time. 4G provides data only and voice is either done by falling back to a different communications model (frequency/"G") or via voice over IP. So when a 3G or 4G signal weakens in a particular area, there is usually a 2G signal to fall back onto but it will only provide voice and text.
There are some interesting notes in the Wikipedia article on 4G if you search for the word "voice". Such as:
EV-DO is not designed for voice, and requires a fallback to 1xRTT when a voice call is placed or received.
And:
Since the 2.5G GPRS system, cellular systems have provided dual infrastructures: packet switched nodes for data services, and circuit switched nodes for voice calls. In 4G systems, the circuit-switched infrastructure is abandoned and only a packet-switched network is provided, while 2.5G and 3G systems require both packet-switched and circuit-switched network nodes, i.e. two infrastructures in parallel. This means that in 4G, traditional voice calls are replaced by IP telephony.
Another thing to note, is that while voice requires less bandwidth, it requires a continuous connection. Whereas data can be packetized. A good discussion of how voice and data share the network (when both are available) is available in the following article on Using data versus voice in an emergency
Best Answer
In most cellular systems the receiver in the handset (mobile, phone, etc.) goes into a low power "discontinuous receive" mode when not actively in a call. It wakes up about once per second and listens to a control channel from the base station it's currently associated with. The operations inside the handset occur at whatever the CPU clock rate is, on the order 26MHz, 38.4MHz,... or higher. The timing at the radio side of the system is fixed to certain symbol rates, but once messages are received the internal processor can operate as quickly as it is capable of (and designed to operate).
If there is an SMS (text) message or a call for the handset then it can be delivered in one of the base station control channel time slots. Since it's a synchronous system, the timing is really governed by the design of the cellular system rather than the handset.
What level of detail are you interested in? Once the message is received, it's up to the phone software to alert you that a message has been received, and that's dependent on what else the phone is doing (schedule priorities, interrupt rate, etdc.).