According to the accounting principles, variable consideration refers to elements of a transaction price that may change depending on future events. In the case of Trust in Law Inc., where 80% of their fee is contingent on the outcome of the court case, the appropriate method to estimate variable consideration would be to use the most likely amount, as this approach better predicts the amount of consideration to which the company will be entitled given the 75% probability of a positive outcome.

On the other hand, for Build Together Ltd., the potential bonus or penalty structure for completing the oil rig construction by a specific date introduces a wide range of possible outcomes. In such scenarios, using the most likely amount might not be the best estimate of variable consideration because it doesn't account for the range of possible outcomes. Instead, the expected value or probability-weighted method might be more appropriate for estimating the variable consideration in this case.

Lastly, in the example of Hotline Crisis Ltd. purchasing telephones from TelTel Inc., since there's no variable price component in the transaction (returning the phones does not qualify as variable consideration under the context of the purchase, only the fixed price per telephone), the transaction price for TelTel Inc. would be considered fixed, with no variable consideration involved.

In conclusion, the treatment of variable consideration varies depending on the specifics of each contract and the predictability of the outcome.