least GSM power in dBm required to send an SMS
"I had a conversation with a network engineer of a respective provider, he advised their cut off point is at -102dBm." 

That is indeed the minimum receiver sensitivity figure for a class 4/5 GSM900 mobile station in GMSK mode. If you wish to read the full performance specs, you may consider downloading the 3GPP TS 45.005 pdf (Old ETSI TS 145.005 ref). 3GPP download. 

Chapter 6 deals with receiver performance. Remember that a test if the receiver conforms is typically done in a lab environment with a radiocomtester like an R&amp;S CMU200 or Agilent 8960. These instruments simulate a GSM base station including signal fading and (Gaussian) noise conditions like present in a real-life situation (patterns &amp; figures specified in the document above). Nevertheless real conditions can still be worse.

Without knowing the actual system details you can always have a very coarse performance estimate of a random radio receiver with the following equation:

$$L = - 174 + 10.log(BW) + NF$$


The BW of a GSM channel is 200kHz.
A realistic receiver noise figure (NF) is 8dB 


$$L = -174 + 53 + 8 = -112 dBm $$

Channel coding, SNR and other factors further influence this figure, either positive or negative.