We've come a long way in the twenty years since the Blackberry was introduced in 2002. Remember the Blackberry? It was amazing. I could schedule meetings on a calendar, and read documents ON THEPHONE! The GPS navigation was super-buggy, but I loved the keyboard.
     Flash forward to today. Cell phones track and transmit medical data, consummate stock trades, send and receive money or cryptocurrency, record your exercise, stream music, movies, TV, and your favorite video games. You can read and post in social media, host videoconferences, compose and transmit documents. You can navigate on the road or on the trail, manage your internet of things, and purchase everything from event tickets to groceries. Oh, and they still make phone calls.
     I won't even pretend to know all that's possible with a smartphone today. But if you can think of something todo with or on your mobile phone, chances are there's an app for that. If there isn't, there will be in another year or two.
     I'm sure you've noticed that smartphones play an integral role in all my EPSILON series books. On Mars, the EVA suits come with a sleeve pocket to hold one. They're connected to the helmet mic and speakers via Bluetooth or comparable technology. A stylus allows for written communication with bulky EVA gloves.
But is it realistic for an away party to communicate with Prospector Base using a smartphone? What about sending and receiving texts from orbiting MGPS (Mars Geo Positioning Satellites)?
     Let's take a quick look at how cellphones function here on earth. They operate in conjunction with a cell--a transceiver with a limited operating range. The phone and tower constantly communicate on an agreed frequency and the tower tracks the signal strength from your phone.
     Adjacent towers also track your mobile phone. As you move out of range from the first tower your signal strength increases at a second. The two base stations coordinate with each other, and at some point, your phone gets a message on a control channel telling it to change frequencies. This handoff switches your smartphone to the new cell.
     The digital signals are broken up into data packets bearing a unique identifier. This allows the stream of packets to be reassembled as the signal forwards to its intended destination. A tremendous amount of data can be transmitted, even during periods of heavy carrier use.
     The different generations of cell service each come with their distinct sets of frequency bands. 3G operates--or rather, operated--at 2100 MHz with a bandwidth of 15 to 20 MHz. 4G uses similar frequencies but with an expanded 100 MHz bandwidth. LTE technology improves the data transmission rate. 5G operates from 2 to 300 GHz. Furthermore, 5G also uses 4G spectrum to enable a lesser service in areas not served by 5G.
     What bands do each major carrier use today?
     Verizon: 850 MHz Band n5 (also used for 4G), 1700 to 2100 MHz Band n66 (also used for 4G), 1900 MHz Band n2 (also used for 4G), 3.7 GHz Band n77, 28 GHz Band 261, 39 GHz Band 260.
     AT&T: 850 MHz Band n5 (also used for 4G), 3.4 GHz Band n2, 3.7 GHz Band n77, 24 GHz Band n258, 39 GHz: Bandn260.
     T-Mobile: 600 MHz Band n71 (also used for 4G), 2.5 GHz Band n41, 3.4 GHz Band n2, 3.7 GHz Band n77, 24 GHz Band n258,28 GHz Band n261, 39 GHz Band n260, 47 GHz Band n262.
     Is a cell phone's operating frequency programmable? Yes. Service techs can google a code to gain access to the programming through the keypad. For the rest of us mortals, we do it via the SIM card. It's why you provide your phone number if you plan to switch carriers, provided your phone is unlocked (i.e., the SIM card isn't linked to the phone's serial number).
     I've used an unlocked 4GMotorola G Power successfully on two different service providers. Here's a partial list of networks--each with their unique licensed spectra. It could work on: AT&T, Boost Mobile, T Mobile, Cricket, Metro TracFone, U.S. Cellular, Verizon, Xfinity Mobile.
     There are at least four transceivers built into phones made today: cellular, WiFi, Bluetooth, and GPS. The MGPS communication frequency used in Crimson Lucre was 400.7 MHz for low data communications. Recall that Allie programmed Dallas's phone to send text messages for relay to Earth at that frequency. MGPS positioning broadcasted at402.5 MHz. Routing the SMS through that antenna was a reasonable course of action for her.
     Let's look about fifteen years into the future. Mars has no magnetic field, so a compass won't work for navigation and tracking. Celestial navigation would be useless during the frequent dust storms. A small constellation of GPS microsatellites would be a low-cost solution.
     NASA and SpaceEx are engaged in a Space race to see who reaches Mars first. It's not unreasonable to imagine either or both would save budget by contracting with  cell phone and network routing manufacturers to provide mission mobile communications services.
    These phones would link to the base radio, rover WiFi, helmet Bluetooth and a Mars version of GPS. They may also have transceivers to enable transmission to satellites positioned for communication with earlier unmanned missions. The trick will be to route messages seamlessly across these platforms, which is where tech from network carriers would come into play. Use of cell phones on Mars is a near-certainty.
     I can see it now. National Cell Service sponsors a Superbowl LXIX halftime commercial that touts your service here on Earth will be as reliable as that on Mars. Oh, the final score? The Arizona Cardinals and the Detroit Lions battle to a 17 - 17 tie.

For further Reading

https://rantcell.com/comparison-of-2g-3g-4g-5g.html#:~:text=THIRD%20GENERATION%20(3G)&text=It%20used%20Wide%20Band%20Wireless,bandwidth%20of%2015%2D20%20MHz.

https://www.verizon.com/about/our-company/5g/what-frequency-5g

https://arstechnica.com/gadgets/2022/09/att-wont-upgrade-older-phones-for-new-5g-bands/

https://www.t-mobile.com/support/coverage/t-mobile-network#:~:text=Ultra%20Capacity%20(UC)%205G&text=Band%20n41%20(2.5%20GHz),Band%20n261%20(28%20GHz)

https://www.etopuponline.com/blog/can-you-buy-a-sim-card-for-an-existing-cell-phone