I work with a Telco and would like to explain a few things about the endless marketing SMS and calls you keep getting on your phones.

Intelligent network, simply referred to as IN is the icing on the cake of every basic telecomms network.
It's the system or group of systems responsible for charging, rating, billing your voice calls, data ,SMS and content.
It consists of various servers and storage systems that are well planned and designed to be redundant, very efficient and work at light speed, hence the Intelligence.

Simple places or ways you notice IN at work on your cellphone are :
1.Checking/Recharging your account balance via USSD(Unstructured Supplementary Service Data)eg *779#, *456#..etc.
2.Billing(Postpaid or prepaid) for voice,sms and data.
3.VAS- Value added Services eg.CRBT( Caller Ring Back Tone), Borrowing airtime,Health Tips and other beneficial SMS
4.Bonuses and Plans

Now, to the part that cause some restlessness and sleepless nights for Nigerians.

VAS
As mentioned earlier, Value added services (VAS), contributes a large chunk to the pockets of most Telcos.
These are the services that would likely flood your cellphones with hundreds of SMSs and even call you countless times trying to get your purchasing power.
You see, these services are not generated by the the Telcos themselves but by hundreds of third party agents(3PPs) whose names I am not permitted to mention.

They are companies from differnet parts of world supplying services through different telcos( MTN ,Airtel, Etisalat), but they do it the approval of the Telcos.
Short codes are used for these services eg. 5382(MISS U) , 4200(BBC News),5852 ( Fitness Tips) , 10938 , 38265( Home Care Tips), Isaiah4vs19 etc.
Same goes for phones calls recieved for telemarketing.They all ride on the Intellignet Network.

Other Domains like PS/CS CORE, MPBN ,IT are sometimes involved in the approval/development of these services.

So,when next you see an SMS or phone call that's from your Telco that's marketing or VAS related , know in your mind that it may not be them directly.

There's so much more but I'll stop here.

Feel free to ask your questions.

Enjoy.