Salam Alpha1 I will try and summarise the permissibility of saying Ya Rasoolllah, see below (taken from other sources)
Those who believe that it is impermissible to say Ya Muhammad! [May Allah bless him and grant him peace] not only say that there are no evidences to support the permissibility, but also believe that the prefix of Ya, can only be used when that person [who is being called upon] is present, as opposed to being absent. The proclamation of Ya Muhammad, or Ya Rasul Allah [May Allah bless him and grant him peace] is not an innovation [bid'a] that crept in after the first three generations, but contrary to modern misconceptions, was initiated and practiced within these generations, as we shall see, Allah willing. Also, the fact that the later generations did proclaim Ya Muhammad! [May Allah bless him and grant him peace] after he death of the Prophet [May Allah bless him and grant him peace], even though there were great distances between them and Madina.
The permissibility of saying Ya! For someone who is not physically present. One of the main arguments used against the believers on this issue, is the one of the impermisibility of using the prefix Ya [Oh!] to someone who is not physically present.
Innovation in the Language
This understanding of the Arabic language [that of not being able to use Ya! For an absent person] is an innovation [bid'a] in Arabic grammar. To the minority holding this view, it appears that this is the only way of accusing the majority of Muslims to be constantly committing an impermissible deed, or even shirk and kufr as others may profess.
Since those Muslims who often claim that saying Ya Muhammad! [May Allah bless him and grant him peace] is shirk, I now propose to examine the views of Ibn Taymiyya on this issue. Why? Well, it is mainly because these very brothers have given Ibn Taymiyya the noble title of Shaykh al Islam, and such, use him as an authority, if not, the foremost, in their attempts to practice Islam as the Salaf [pious predecessors] did.
Ibn Taymiyya writes: When someone calls upon someone else, saying Ya! it may be used in one of two ways - physically or by the knowledge of that person. An example of this is when the Messenger of Allah [May Allah bless him and grant him peace] warned the people at the time of Dajjal: "Yaa 'ibaadillaahi Fathbutu…" (Oh servants of Allah! Keep your feet steadfast…) The Prophet, Allah bless him and grant him peace, said this to the people who would be present at the time of Dajjal, and who were not yet born.
Another example, is when Sayyidna 'Ali, may Allah be pleased with Him, was walking through the plain of Karbalah, he said 'Ya Abu 'Abd Allah Hussayn, Fasbir! [Oh, (my son) Abu 'Abd Allah Hussayn! Be patient (when facing the enemy in this place]' This was because 'Ali, may Allah be pleased with Him, was informed by the Messenger of Allah, (May Allah bless him and grant him peace), that his son, Hussayn [May Allah be pleased with Him], would be martyred at Karbalah. Sayyidna 'Ali, may Allah be pleased with Him, called Hussayn despite the fact that he was not present with him, and even though Hussayn could not hear his Father 'Ali, may Allah be pleased with Him, but remained in his thoughts.
[Ibn Taymiyya, Minhaj-as-sunna, chapter Aswad-al-Qadeem]
The above example demonstrates, as provided by Ibn Taymiyya, that at least in one way, Ya can be used in the Arabic language to call someone who is not physically present, but who is present in the thoughts of the caller, as when Sayyidna 'Ali, may Allah be pleased with Him, remembered his son and called to him.
Evidence to support the permissibility of saying Ya Muhammad! [May Allah bless him and grant him peace]
Hafidhh ibn al Qayyim writes that the Prophet of Allah, (May Allah bless him and grant him peace) said: Send salutations on me, but send more salutations on Friday. When you recite the salutation, your voice will reach me wherever you are. Some companions asked, " even after your death?" The Prophet, (May Allah bless him and grant him peace) replied, "Allah has made it unlawful for the earth to decompose my body".
Hafidhh ibn al Qayyim writes that the Prophet of Allah, (May Allah bless him and grant him peace) said: Send salutations on me, but send more salutations on Friday. When you recite the salutation, your voice will reach me wherever you are. Some companions asked, " even after your death?" The Prophet, (May Allah bless him and grant him peace) replied, "Allah has made it unlawful for the earth to decompose my body".
[Hafidhh Ibn-al-Qayyim, Jala-ul-Afhaan page 145]
Imam Nasa'i narrates that there are specific angels who visit the earth and whose sole duties are to go to the persons who sends salutations upon the Prophet Muhammad, (May Allah bless him and grant him peace), and then to take those salutations to the Prophet Muhammad, (May Allah bless him and grant him peace)
[Mishkat chapter on Salaah al Nabi]
The above mentioned Ahadith, indicate that if anyone were to send salutations to the Prophet, (May Allah bless him and grant him peace), he himself would either hear the salutations, or an angel will convey them to him. In both cases, salutations will reach the Prophet, (May Allah bless him and grant him peace).
The Salaf used to say Ya Muhammad! [May Allah bless him and grant him peace]
Imam Bukhari, Hafidhh Ibn Taymiyya and Qadi Shawkani all posed the same question, that if a person's foot becomes numb, what should he do? Their recommendations were the same, and included with their answer, the following hadith:
Some time after Rasul Allah, (May Allah bless him and grant him peace), had passed away, 'Abd Allah Ibn 'Umar [May Allah be pleased with Him] was in Najd where one day his foot became numb. As a remedy to alleviate the pain, a person said to him. "Remember the one whom you love the most!" Upon hearing this Ibn 'Umar [May Allah be pleased with Him] said "Ya Muhammad! [May Allah bless him and grant him peace]" and his foot made an immediate recovery from numbness.
[Imam Bukhari, Adab al Mufrad al Kalim al Tayyab; Hafidhh Ibn Taymiyya and Qadi Shawkani, Tuhfah al Dakireen chapter on Khadirat Rijluhu, and also Imam Nawawi's Kitab al Adkar]
Hafidhh Ibn Taymiyya writes, In the same way as 'Abd Allah ibn Umar's foot became numb and he remembered the one he loves the most, 'Abd Allah Ibn Abbas's foot also became numb. Someone also said to him to remember the one who he loves the most, whereupon 'Abd Allah Ibn Abbas said Ya! Muhammad [May Allah bless him and grant him peace] and his foot immediately recovered from numbness.
[Hafidhh ibn Taymiyya, Al Kalim al Tayyib chapter on Khadirat Rijluhu]
Qadi Shawkani writes: If one is in trouble or is in distress, he should perform two nawafil rakats and then make a supplication. They should say ''Ya Muhammad!'' [May Allah bless him and grant him peace] and Allah most High will grant them what they requested and their problems and troubles should be resolved. The scholars of hadith say that this hadith is authentic and Tirmidhi, Hakim, Nasa'i, Ibn Majah and at-Tabarani record it.
Hafidhh Ibn Kathir, Imam Tabari and Imam Ibn Athir all wrote [that]: During the Khilafa of Abu Bakr as- Siddique, may Allah be pleased with Him, there was a battle against the false Prophet Musaylima [of Najd]. When the battle commenced, the Muslims lost their footing at which point Khalid bin Walid, may Allah be pleased with Him, and the rest of the companions called out "Ya Muhammad!" [May Allah bless him and grant him peace] and proceeded to win the battle.
[Tarikh at Tabari, Tarikh Ibn Kathir and Tarikh Qamil by Imam Tabari, Hafidhh Ibn Kathir and Imam Ibn Athir and Ibn Jarir in Chapter Musaylima Kadhaab]
Hafidhh Ibn Kathir and Imam Tabari both write that After the occasion of Karbala, Sayyida Zaynab, May Allah be well pleased with her, [the sister of Hussayn, may Allah be pleased with Him] and her company were taken as prisoners to Syria. When she passed the dead bodies she proclaimed: "Ya Muhammad!" [May Allah bless him and grant him peace] Your Hussayn is drenched in blood without a shroud or a grave, and Ya Muhammad! [May Allah bless him and grant him peace], your daughters are taken prisoners and your children have been killed
[Ibn Jarir and Tarikh Ibn Kathir in Chapter of Karbala*]
*For those of us, who have forgotten, Karbala took place in Iraq in 60AH. At that time Zaynab may Allah be well pleased with her, said 'Ya Muhammad! [May Allah bless him and grant him peace]
Therefore it is not shirk to say Ya Muhammad, as it has been demonstrated through the above narrations.
I hope this answers your question.