Cell Phone Interface for PBX use

Cellphone interfaces for PBX are
a good way to reduce costs

After realizing that over 50% of the company's cell phone bill is due to local to mobile calls I decided to investigate the possibility of using a Cell Phone Interface for our PBX (generaly called PABX in Brazil).


We have a Digital Telephone Central model Intelbras 141. Which, according to the companies website, supports the ITC 4000 Cellphone Interface.


However, this model is priced nearly twice as much as a model from a different manufacturer (Naccell, ITS, Plugcell).


These are said to be compatible with *any* PBX on the market, however I fear they might only be compatible with Analogic or Hybrid Telephone Centrals.


Another issue involved is the selection of the carrier plan: one major catch here: STATIC USE CLAUSE.


Most carriers, on their general purpuse plans, have a clause on their contract stating the following (extracted from TIM contract for a Liberty plan) that is said to void the contract and cause loss of benefits:


3.3.1.3. Uso estático (sem mobilidade) do aparelho celular em cerca de 60% do tráfego originado pelo CLIENTE e recebimento de ligações em proporção inferior a 33% do volume originado, por
mês.


Meaning:


3.3.1.3. Static Use (no mobility) of the celular device in around 60% of traffic originated by the client and receival of calls in proportion inferior than 33% of the originated volume, each month.


With that in mind, I have to find a plan that does not forbid you from having a staticaly allocated sim card carrying calls for my PBX.