So if you are pretty sure what you are doing (say, you know your phone can handle 500k at least, the recipients phone can do so as well, and both your carriers support it), increasing the limit might enable you to exchange MMS up to 500k with that recipient - while failing to do so with others. Consider the 300kB limit as 'smallest common denominator' between your phones capability, your carriers capability/configuration and the receivers capability.
As Zuul pointed out (see comment below), you may then be able to successfully send a message of, say, 1MB size - but that doesn't necessarily mean the recipient is able to receive (let alone read) it.
Sure one can alter any limits, but usually there's a good reason for their presence. For your second question, you might want to check Manually edit your max MMS size limit.Īs for changing the limit, there are several consideration to be taken. The maximum size for MMS is rather carrier-dependent, and usually is set to 300kB.
