The main disadvantage of all methods listed above is that they require the possibility to place an order while most of the traders using trading signals could be outside of their trading workplace most of the time. In such case, they will miss trades just because they have no access to the trading platform.
To my mind, it would be better to use a solution that directly transform signals into ordres. For example, you can check Forex Copier and its Remote version in particular. It offers the possibility to recieve signals amending them according to the account size and risk settings. Actually, it requires both provider and reciever parts installed, but I think it is not a problem.
At the same time, providing signals via channels mentioned above, in the form of text messages, gives additional flexibility, because it is possible to evaluate the situation and either to follow a particular signal or just ignore it. But keep in mind that using such approach may lead to missing both losing and winning signals, so the win rate of the strategy may change. That is why it would be better to execute trades upon all the signals from the provider if you trust him (otherwise you should not use his signals at all).