Bring Your Own SIM Card

comma 3, 3X & comma 4

All comma devices have a built-in LTE modem and nano-SIM slot. You're not locked into comma Prime — you can use your own carrier SIM. Here's what you need to know, including how to physically access the SIM slot on the comma 4.

Setup Flow

The BYOS process in four steps

Confirm the hardware

The Snapdragon 845 SoC used in every comma device includes an integrated LTE modem, and each device has a nano-SIM slot. comma Prime provides the managed SIM and data plan, but using your own carrier SIM is supported with some caveats per device.

Insert the SIM

comma 3 and comma 3X have a tool-free side slot. comma 4 is different: the nano-SIM slot is internal and was discovered during a community hardware teardown, so physical access requires carefully opening the device.

Configure the APN

After inserting your SIM, configure the APN for your carrier. Without the correct APN, the device may show a cellular signal but have no data connection.

Validate connectivity

If you see the Weedle Wi-Fi hotspot but have no data, this almost always means the APN is not configured. The modem is active but cannot reach the carrier data network.

Hardware Access

Which devices have a SIM slot?

All comma devices have built-in LTE

The main difference is how easy the SIM is to access.

Device	SIM Type	Physical Access	eSIM
comma 3 (C3)	Nano-SIM	Side slot — tool-free	No
comma 3X (C3X)	Nano-SIM	Side slot — tool-free	No
comma 4	Nano-SIM	Internal — requires opening case	Present but not available for 3rd-party use

comma 4

Accessing the internal SIM slot

Internal SIM

Not officially supported

comma 4 requires opening the case

Unlike the C3 and C3X, the comma 4 does not have an externally accessible SIM tray.

The nano-SIM slot is internal and was discovered during a community hardware teardown. Opening the comma 4 case is not supported by comma.ai and may affect your warranty.

The Taiwanese community teardown video documents the procedure. Review it fully before attempting: search “comma 4 teardown SIM card” on YouTube. We are working to confirm the exact URL. If you have it, please share in the comma Discord.

The comma 4 has eSIM hardware, but it is not currently available for third-party use. The eSIM is used exclusively by comma Prime. Until comma.ai opens eSIM provisioning to users, a physical nano-SIM is the only third-party cellular option.

APN Configuration

Set up the data connection after the SIM install

Common carrier APNs

If you see the Weedle hotspot but have no data, the APN is the first thing to check.

Carrier	APN	Notes
T-Mobile	fast.t-mobile.com	Works for most T-Mobile MVNOs
AT&T	phone	Or 'broadband' for some plans
Verizon	vzwinternet	May require carrier whitelist
Google Fi	h2g2	Uses T-Mobile/US Cellular networks
Mint Mobile	fast.t-mobile.com	T-Mobile MVNO — same APN

Configuring APN via SSH

1. SSH into your device via comma connect or local Wi-Fi.

2. Check modem status: mmcli -m 0

3. Configure APN: mmcli -m 0 --simple-connect="apn=YOUR_APN"

4. Verify data: curl -s https://ipinfo.io

comma.ai has an official guide for replacing the SIM in a comma 3X: comma.ai/shipping. Search for “How do you replace the SIM card in a comma 3X?”. After inserting a new SIM, the device needs Wi-Fi for activation. That can take about 5 minutes online plus up to 30 minutes total, and may require a reboot.

Comparison

comma Prime vs bring your own SIM

Feature	comma Prime ($24/mo)	Bring Your Own SIM
Setup	Plug and play — SIM included	Physical install + APN config required
comma 4 access	Managed — no case opening	Requires opening the case
Drive log storage	1 year via comma connect	3 days only
Remote snapshots	Included	Not available without prime
comma support	Officially supported	Not supported by comma
Cost	$24/month (US & Puerto Rico)	Your carrier rate
International	US & Puerto Rico only	Any carrier that works on device

Bottom line: comma Prime is the easiest, most reliable option for most users. BYOS makes sense if you're outside the US, have a cheap unlimited plan, or need to avoid the subscription. On the comma 4, BYOS is significantly more involved due to the physical SIM requiring case opening.

Troubleshooting