I would comment that attempts to avoid tracking are quite futile.
As Estel pointed out, there are "keep-alives".. those are actually called Location Updates (although their resolution is quite limited); there are data network versions called Routing Area Updates.
There are *many* other ways to know where your cell phone is, and it is a must. Else, the telco network wouldn't be able to ring your phone when a call comes in, or do other stuff.
I've also heard of methods called Geo-Location Tagging (probably won't appear on google) which is quite accurate.
SMS is only on the circuit switched network; the packet switched network, if your turn on your data connection, would open another circuit from your phone to the telco network, providing one more circuit that can be tracked from the operator network.

You can go look up signalling that happens between the phone & operator network under GSM, GPRS, 3G (HSPA), etc signalling.

The only way to be sure you are not tracked is to turn off your phone.

kh