Bryant made a super-helpful explanation to a question asked almost 2 years prior to the time I am currently reading it, so I'm not sure if the OP will ever read this response. But for all you future people, there are a few other important points to be made, based on the rules in the compendium (DnD insiders) as of this posting date:
The rules on readying an action require a very specific mention of when the readied action triggers, and you do not get to make your readied action until the specified trigger occurs (and only if you decide to do so). You are at the mercy of the trigger occuring. This is in distinct contrast to when you choose to delay a FULL turn, where you can re-enter the initiative order and take your turn after any other creature's turn until your prior initiative reappears. Therefore, in readying an action in this situation, you are risking completely losing that action, in which case your initiative would remain the same. Indeed, it's up the DM both as to whether the trigger is specific enough, and whether to make the circumstance causing the trigger occurs in the first place.
To illustrate what happens exactly, I'll describe an example, and all possible occuring cases. I will make the following assumptions: Your initiative count is at position #3, and there are 26 creatures / objects that act in initiative. Additionally, you choose a trigger and ready your action during your second turn (the third turn of round 2), having cast Wall of Fire on your first turn ( the third turn of round 1).
Case 1: The trigger doesn't occur before the initiative count returns to 3 on the third round, that is, before the initiative count again returns to your originial initiative. You have effectively lost a standard action from the second round, and the duration of the sustain effect has not increased in total number of turns of existence.
Case 2: The trigger occurs before the initiative count returns to your originial initiative on the third round.
---->Case 2a: You choose not to take the readied action when the trigger occurs (say for example all other creatures are dead and you don't want to waste your encounter power). The effect is similar to the effect from Case 1, except you only waste a single standard action from round 2, and are not forced to also waste the encounter power.
---->Case 2b: You choose to take the readied action when the trigger occurs, and the trigger occurs on the turn immediately after you ready your action (still on round 2). Your initiative doesn't change because your turn was already immediately before the turn you interrupted, and your future turns function as it normally would have. You do not effectively lose the standard action, nor do you wait longer to take actions on your next turn. The sustain duration from your turn on round 2 is unaffected by your readied action.
---->Case 2c: You choose to take the trigger, and the trigger occurs any time between 2 turns after you readied your action and the turn before your initiative returns on round 3. (i.e. Case 2 is true, but Cases 1, 2a and as 2b are not). Your initiative resets to immediately before the interrupted creature's turn. You must wait longer for your next turn than you would have without having taken the readied action, and your sustained effect persists during that same amount of time. While the sustain duration is technically longer than it would have been without taking the readied action, this effect is balanced by preventing you from taking a full set of actions for a longer time.
I will use the most extreme example to visually illustrate what *CASE 2c really means below*
"A" represents the person who was assigned initiative count 1 during round 1, "B" respresents the person with initiative 2 during round 1, "C" represents you (with initiative 3 during round 1), et cetera. The following format visually depicts the order each round:
Round #: A (Turn # Person A took that round), B (Turn # Person B took that round), ..., Z (Turn # Person Z took that round).
Round 1: A(1), __ _ B(2), C(3), ..., ..., ..., ..., ..., Z(26)
Round 2: A(1), __ _ B(2), C(3), ..., ..., ..., ..., ..., Z(26)
Round 3: A(1), C(0), B(2), D(3), E(4),..., ..., ..., ..., Z(25)
Round 4: A(1), C(2), B(3), D(4), E(5),..., ..., ..., ..., Z(26)
Round 5: Same as Round 4.
** In Round 1, you, player C, cast Fire Wall during the third turn of the first round, depicted as C(3).
** In Round 2, you, player C, sustain your fire wall, and ready an action during the third turn of the second round, depicted in bold as C(3).
** In Round 3, during creature B's turn, the trigger occurs, and you decide to take the readied action at that time. The interrupted creature's turn is depicted in bold, B(2).
**At the time you take the readied action, your initiative has now reset to a position immediately before creature B. Because your initiative has passed for this round, you lose your turn in round 3.
**Creature B has technically taken its turn for round three, the second turn for round 3, so C(0) is inserted, in italics, as a placeholder to represent your new position in initiative, but also to reinforce that you do not act in that round. You can see, therefore, because you lose your turn, there are only 25 turns in round 3.
** In Round 4, the initiative order has been reset, there is a new order, and there is a full number of turns in the round. Your new position in this round is depicted in bold, C(2), representing the next turn in which you have a full complement of actions after delaying your action in round 2.
** Note that by delaying in this manner, you have effectively waited almost 2 rounds before taking another full turn, exactly 50 turns (23 turns in round 2, 25 in round 3, and 2 in round 4). At the same time, your sustain effect has lasted for 50 turns, 24 more turns than it would have if you had not delayed your turn. You get the same number of "bonus turns" on your sustain effect as you do "penalty" turns without a full set of actions. This is also 24 turns longer to wait for a full set of actions than if you had lost your readied action, as in Case 1, or chosen not to take the readied action, as in Case 2a!!!
---> Here you can clearly see that the more time it takes for your readied action to trigger before your original initative returns, the longer you will be without a full turn (assuming you decide to take the readied action).
**If you decide to take your readied action on a trigger that occurs on the last possible turn before you lose the action, as in the example above from Case 2c, you will have the max number of turns without taking a full set of actions. In this extreme maximum case, your next fully function turn after delaying occurs (MAX) turns after it otherwise would have had you not taken the delayed action, where (MAX) = (Number of creatures in the initiative - 2). Remember, had you not taken the delayed action, and let it go to waste, you would have waited a full round (only 26 turns), as normal.
**If you decide to take your readied action on a trigger that occurs on the turn after you delayed the action, as in case 2b, you will have the minimum number of turns without taking a full set of actions. In this extreme minumum case, your next fully functional turn after delaying occurs 0 turns after it otherwise would have had you not taken the delayed action, meaning that the turn order is NOT affected, and you wait a full round as normal.
If you have followed the discussion this far, it should be clear that the benefit of taking a readied action when it triggers must be carefully weighed against the corresponding sacrifice you must make in turns without a full set of actions available to you. The sacrifice is greater the more turns it takes to trigger after you delay, and you can always choose to ignore the trigger, so you may be inclined to electively lose the delayed action in favor of taking your next turn normally, depending on how badly you need to take the delayed action, when you would take it, and how many turns without more actions you would lose as a result.
